Also consider swinger or "Lifestyle" clubs where people meet for sex. Now, if that makes you nervous, here are a few things to know about them:
1) Socializing comes first: Most nights the majority of the evening is spent with couples just hanging out with each other. Most of the sex happens later
2) Swapping / orgies are not as prevalent as you imagine: For many couples the excitement is in the exhibitionism / voyeurism, though many are interested.
3) Rules are in place (and enforced) to keep unicorns like yourself feeling safe and comfortable. All you have to do is go to the staff and say "that person / couple keeps asking me to join them and I've already told them no" and those people will be ejected from the club.

A unicorn like you will likely find one or more couples of similarly attractive people looking for someone like you. I've only been to a club where I live a couple of times, but each time there were attractive 20's something couples who met up with similarly attractive, unattached women.

Having actually met and liked the couple in question, why not write to them now?

Granted, it's much easier for a gay man than, maybe anyone else, but if it were me might start by telling a story of something similar. I might tell them they reminded me of this hot couple I had a 3 way with on a cruise, which gets across the point that you find them hot and that you are game for 3 ways. You could also mention that you find it easier to be experimental with people from another city, which will help remind them they can play with you without seeing you at church every Sunday after. After that you have to read the room. If one seems interested and the other not, skip it. If they both clearly seem interested, maybe you make a more pointed offer, maybe while the husband is away.

Just get em drunk. It's the wedding way.

What polyphemus @2 said! Post-wedding, fly-out-there scenario? Could be super hot.

One other thing that might be worth considering, if you find a hot couple you vibe with out there 'in the wild', and especially if they're into the idea but perhaps never have done that before, they may not have figured out what their couple-rules are around getting frisky with a unicorn.
Once your back at their place have a pre-sexytimes chat, might be worth making them use their words and asking what their boundaries and limits are. Also a good time to disclose STI status of course too, ;>) Be brave! They'll be nervous too.

THIRD is right to be apprehensive. I remember a Carolyn Hax column several years ago when a (lonely, single) woman asked whether she should ask a couple with whom she was close friends for a threesome, or possibly a triad, I don't remember. Many of the comments were "I'd drop her as a friend." I was surprised by this -- I got that many couples wouldn't be into the idea, but surely, just take it as a compliment and move on? I asked commenters to elaborate, and they said they would view the request as a thinly veiled attempt to sleep with the husband. From that, my advice to THIRD is find out whether the woman is bi before making a move. (Of course, in this situation THIRD doesn't have close friends she stands to lose, but still. If some straight women would react this way it's not worth risking, IMO. Besides, the threesome wouldn't be anywhere near as much fun if the gal was straight. Probable jealousy issues. Anyway, I digress...)

Anyway! I agree with Poly (heh) @2. If there was chemistry, THIRD should e-mail the couple and proposition them in a friendly, flirty note. E-mail them both together, then there's no awkwardness about hitting on one behind the other's back. Offer to go visit them; book a hotel room in case things go wrong (as my first MFF threesome did...); go out for a boozy meal, and have fun. Besides, if they do say no, you won't feel as awkward because you won't run into them socially. In fact this seems the perfect opportunity to practice your propositioning. Good luck, THIRD -- and report back! :D

@5 - *you're back at their place...

Treacle @5: The pre-sexytimes chat should be at a restaurant or bar, not at their place, where she could feel trapped if things take a creepy turn. But absolutely, everything should be discussed -- rules, experience, boundaries, safewords if necessary (they're not just for BDSM play), STIs, any other relationships the unicorn is in. Back at their place, discuss what activities who wants to do with whom. Enthusiastic consent and no misunderstandings!

(Waa. I was halfway to a threesome a few weeks back... now I'm envious of THIRD. Go, THIRD! Get some for me! haha)

@7 Thank's for that. The missing apostrophe hit me like a 2x4 between the eye's.

"You're both so hot and if you're ever looking for a third..." If they bite, yahtzee."

Not necessarily...

"You're both so hot..." is enough to test their interest. Let them do some of the work.

@6 I was invited to be a THIRD once. It actually put me off and I felt that the couple (the wife is my ex from college a lifetime ago) kind of tricked me into coming to their house (late at night and deep in the woods; with multiple comments about 'not having neighbors') and I wasn't sure they had a particular interest in the me that wasn't having sex with them. It's probably a similar feeling to that guy you've been friends with forever reveals he's always had a thing for you or whatever. So while I didn't blow up (I beat an awkward retreat), I feel like I need to keep my distance and only engage in places where it's difficult to be propositioned (and or it's not 10pm and I'm starting at a 90-minute drive home).

So, you know, it's not that weird that so many folks would react negatively to being propositioned, regardless of where they are in the triangle.

THIRD, nothing ventured, nothing gained has to be your motto. You generally don’t get what you don’t ask for, so remember to ask for what you want. That said, a deft, flirty touch is a good technique for the shy, and worth practicing and mastering.

I wouldn’t feel too bad about this as a missed opportunity, as my sense from the set up is that your couple was not either not experienced in having threesomes or they were in fact not into you. If they were experienced in threesomes they would probably have some skill at seducing thirds which suggests a lack of interest if they didn’t make any effort to get you into bed. If they are inexperienced at threesomes, you may have correctly sensed their sexual attraction to you, but they may not have worked out any ground rules between them for such a circumstance. Given your own inexperience with threesomes, you may very well be better off angling for a threesome with them now, when the ground rules can be established before your clothes come off.

@6 Mostly agree but THIRD should initially contact only the wife, not the husband, thus giving her the opportunity to decline without potentially creating drama between the two of them.

SA @12

my sense from the set up is that your couple was not either not experienced in having threesomes or they were in fact not into you

Third possibility: this couple was not interested in threesomes. It's not everyone's ultimate fantasy.

Sporty @11: Thanks for the backup. I was beginning to feel I was overstating the safety/comfort aspects compared to the fun potential, based on my own early experience with a woman whose boyfriend I'd agreed could "watch," but who ended up raping me, with her collusion. The lesson from that was that if you don't desire both people equally, don't put yourself into a situation where your boundaries may not be respected. As another sage SL commenter said recently, "No one is making sure the unicorn gets the long end of any stick ever."

Sublime @12: I'm experienced at threesomes and still have no skill whatsoever in seducing anyone with a vagina. It's a really awkward ask, no matter who's doing the asking. The couple may have not wanted to make THIRD feel uncomfortable at the mutual friend's wedding, or they may have assumed she was one of the overwhelming majority of women who don't want to be a unicorn.

MarciaX @13: Disagree for reasons of potential provocation of jealousy. Threesomes work best when everyone is equally into each other. If THIRD e-mails the wife behind the husband's back, the husband may (understandably) think THIRD's main interest is in Wife and feel threatened. In other words, no matter how this is broached, drama may result. (If the proposition was made in person, I'd agree -- ask the wife first -- but with electronic means she has the opportunity to express interest in both of them.)

I'm going to come out and say no, don't proposition married people for sex (jointly or separately) unless you know they aren't monogamous.

@5 I don't think trying to find out if the woman is bi makes a difference. I'm not sure either my wife or I would necessarily identify as bi but I do think if the person (a unicorn) and situation (away at a wedding) were right we'd be game. Asking really is the best thing and seriously, if it gets torpedoed, so what? You're likely to never see these people again.

Plus I love the idea of reconnecting to see if there was a chance and then flying out there. Could be worth it. And if that doesn't work then you can give the LW my wife's email.

TS @16: I agree that the proposition should include an acknowledgement of "I don't know if your relationship is open to any extent, but if it is..."

@16 and @18

Yes. If you don't ask you won't know. It's all about consent. If they say, "no," then you move on. Don't persist and be creepy. On the other hand, how are you supposed to know if a couple in that sitch is game if you don't ask?

You never know how anyone is going to react to any given pass, but if these people were both "friendly" to you, I'd say, "What the hell, give it the old college try." But definitely approach the wife first in the in-person situation. In most heterosexual situations you're poaching in her territory. Unless you've vastly misinterpreted their interest, the worst you're likely to get is an amused, "Thanks, but no thanks." Personally, I'd take it as a compliment, even if I wasn't interested. Email them both if it looks like you're going to bump into them again in the future.

@14/Registered European: "Third possibility: this couple was not interested in threesomes. It's not everyone's ultimate fantasy." Mentally, I had put that under the category of "inexperienced," an inexperience borne of lack of interest. But I agree that THIRD needs to understand she may wants to be someone's unicorn, but some people don't want a unicorn. Of course, I already lost the argument with Dan and others in the comment section that you can't declare yourself a unicorn, only the couple that wants you can bestow that appellation on you.

@15/BiDanFan: "I'm experienced at threesomes and still have no skill whatsoever in seducing anyone with a vagina." I recommend that you contact internationally known sex advice columnists Dan Savage. Call the Savage Love Podcast at 206-302-2064 or email Dan at mail@savagelove.net.

@21: I don't think seducing vagina-havers is one of Dan's strong suits.

@22: Yes, I do believe that it was once appropriate to address Dan as something like "hey, man-with-no-interest-in-vaginas" - which leads me to believe that seducing vagina-havers is not his area of expertise.

Bostonius @19: To follow up, how are you supposed to know whether the couple is even "in that sitch" unless you ask? Couples in opposite-sex relationships are generally presumed to be straight and monogamous, but this is not always the case. Unless you met them at a swingers' club or poly retreat, you have no way of knowing other than asking. (How to ask without feeling awkward... well, if someone perfects that script, they'll make a fortune.)

Would it be weird if a unicorn were to have a pin or detachable patch of a pretty rainbow unicorn somewhere on them? Like on a jacket or handbag? If someone were to ask about it and a) they were part of a hot couple, she could explain the significance ("it's a term for bisexual women who are open to being with couples") and see where the conversation goes, or b) if they were not a couple she were interested in, she could simply say something like "I just really like unicorns" or "I was obsessed with Lisa Frank as a kid." Or is that a monumentally stupid idea? Genuinely asking, since that was what I thought of when I read the letter.

...regardless, drawing a pretty rainbow unicorn sounds fun now. I might make such a drawing and put it in my Etsy shop in some form just for fun.

Or also c), she could point out the decoration to a couple she's interested in and use it as a conversation starter.

@25/26 ~ Here's a pretty rainbow unicorn balloon. She could tie it to her wrist and then people would be able to spot her from a distance in a crowd. Unicorn! Get your UNICORN here!
https://shop.studiodiy.com/shop/rainbow-…

I represent heteronormative culture (I was nominated spokesperson at The Elbo Room on spring break in 94). Unicorn needs to play the odds:

Odds are the husband will say yes. It's universal that men want a threesome with two women. Ok, I suppose he could say no, just like a woman might say no if someone offered to clean their house - it seems too good to be true.

Odds are the woman will be the gatekeeper because 1) she may not be into women; or 2) she views unicorn as a man-thief or 3) she doesn't like the idea of her husband having sex with another woman.

Secure the wife's approval, and you are 95% home. Plant a steamy kiss on wife in front of husband and let the hijinks begin.

@9 fubar: I enjoyed this comment so much I sent a screenshot to a friend.

Ugh. I'm imaging that my husband and I are at a friend's wedding and we start chatting with a single woman who's also attending. We're all having a nice time, exchanging pleasantries and all of a sudden she propositions the both of us.

Dude.
Not every straight couple (or same sex one) wants any kind of non-monogamy.
Not every woman is down for having sex with another woman.
Not every friendly conversation is an invitation to have sex.

There's an attitude of entitlement and superiority in this letter that is so off-putting. I think it starts with the "unicorn" self-labeling. You don't get to decide whether or not you're a unicorn. Someone else has to make that designation.

Nocute @30: Would you "ugh" a request for a date from a single man whom you weren't interested in? Or would you politely decline?
Asking is just that, it's a question. They could say yes, they could say no. I suspect THIRD can tell the difference between friendly conversations and flirting; most of us have at least some ability to read signals by the time we reach our mid twenties.
And a "unicorn" is defined in popular slang as a bi woman who is interested in having threesomes with MF couples. Why should a woman who fits this description not be able to describe herself as such?
THIRD says, "I'm struggling with how to broach the subject with a couple when the encounter happens organically in real life ... for fear of coming off as a creep." Doesn't sound the least bit entitled or superior to me.

But, thanks for helping prove the point I made @6.

@27 DonnyKlicious - welp, that's why I was asking.

@BiDan: I just found her presumptuous. I understand there is a fine line between friendly conversation and flirtation, and obviously the lw knows better than any of us do how much sexual interest was being signaled versus how much she found the couple "UNBELIEVABLY hot," and decided that because she was into them, they must have been into her and the only thing holding them back was the realization that "different couples have different arrangements, and hitting on what might have turned out to be a monogamous married woman in front of her husband could (understandably) be seen as pretty douchey." Well, what if the woman in the couple wasn't bi, but was straight. Even if the couple isn't monogamous, the woman may not be interested in another woman sexually, and can still have enjoyed her company.

I guess I get really tired of the culture implying that all women are sexually fluid or bi-curious, if not fully bi-sexual, mostly because that fits some straight man's fantasy. I don't mean that plenty of women are sexually fluid or bi-curious or heteroflexible or bisexual, but not all of us are. If I had been at a weekend wedding with my husband, the odds are good that I would have hit it off with a woman in a friendly way, and if she then made the dual assumptions that I was into her sexually and would welcome a threeway between her and her husband, I would be really taken aback.

@BiDan, you asked: "Would you "ugh" a request for a date from a single man whom you weren't interested in? Or would you politely decline?" I could politely decline whether the ask came from a single man or woman or a couple, of course. But if someone asked me out on a date, I would assume (perhaps mistakenly) that he was interested in starting some sort of relationship with me as opposed to just getting laid. The lw is talking about asking out a married couple who may be monogamous (indeed, that is generally the default presumption), and are in any case likely not openly on the dating market, or at a dating event or in an environment where it is assumed everyone is interested in dating each other, and furthermore, she's not talking about asking to go out with them--she's talking about asking to fuck them. All the lw wants is to have sex, and it didn't seem that she was asking how she asks for anything but to get jointly laid.

Oh my God Tim Horton @28 it is not universal that men (did you mean heterosexual men maybe?) want a threesome with two women.
The only threesome my husband is interested in is with me and another man. Not that we've had any kind of threesome, but his fantasy life is definitely about adding another penis to the current formula. I think a lot more so-called straight men are bicurious than you probably realise.

@25: I imagine it’d get more creeper attention than positive in the world we live in, sadly :(

I was once on the couple end of a unicorn semi-proposition, except that she made it sound like it was all our idea. We met her through work, and invited her over for dinner. She was a highly intelligent, very interesting person and she was involved in some of the same causes we were, so we wanted to get to know her better. After supper, as we were hanging out and talking in the living room over a second bottle of wine, she leaned forward with a big grin and said, "So. Did you guys invite me over here for a threesome, or what?" My spouse and I, wide-eyed and caught entirely by surprise, said, "No!" almost in unison. "Oh," she said. "Sorry. It just seemed to me like it might be that kind of a setup." And that was the end of it. She relaxed back into her chair, and we just continued to talk and laugh and enjoy each other's company for the rest of the evening, with no awkwardness (at least, none that I noticed). She transferred to another city shortly thereafter and we eventually lost touch with each other, but before she left, we continued to see each other at work and in social gatherings. She was, and I'm sure still is, a very cool person. It was clearly a case of mistaken assumptions, but one that was easily corrected with one direct query. To this day, I'm not sure if she wanted to cut the small talk and get to the threesome action, or wanted to tell us that she was definitely NOT the unicorn we were seeking...and at this point, I suppose it doesn't really matter. She asked, we said no, minimal drama, end of story.

But, you know what? If we HAD been interested in a threesome that night, it would have still been the right question - only our answer would have been different. So I would advise THIRD to go for it, assuming she can tolerate the possibility of rejection.

@BiDan 31: At a wedding, with my husband, if another man propositioned me? "Ugh" would be a very mild response. "I am literally here with my husband, what is wrong with you," would be more likely.

Nocute @34: "Well, what if the woman in the couple wasn't bi, but was straight. Even if the couple isn't monogamous, the woman may not be interested in another woman sexually, and can still have enjoyed her company." That is exactly the point I was making @6. First, find out whether the woman likes women. If she doesn't, it's not worth risking a reaction like yours. And asking isn't "making assumptions," FFS. If I meet, for instance, a man with a beard, and we get along and he asks me out, is that "making assumptions" that I like bearded men (which I absolutely do not, but how does he know that?) -- that all women like bearded men -- or is that just asking because if there is no asking, there is no getting?

Loads of men ask for "dates" when all they want is sex. I can't believe you haven't experienced this.

Busy @36: And loads of men are either insecure or naturally monogamous. Trust me, I've dated them. The idea of a threesome meant "you're going to leave me for a woman." The desire is not universal. I'd amend Tim's premise to: The guy is far more likely to want the threesome, unless the woman is bi, in which case she's far more likely to want it and he's far more likely to veto. The advice -- approach the woman first -- is sound.

Traffic @39: "With your husband" was not the hypothetical situation I was describing, but thanks for your input.

TH @28

It's universal that men want a threesome with two women.

This again? *eyeroll*

BiDan: if the situation was that I was at a wedding with my husband and we hit it off in a friendly way with a single man who was there and enjoyed chatting and whatnot over the course of the weekend, and he propositioned us à la THIRD's letter ("is there a standard, polite way to ask a hot couple if they would be interested in fucking me?"), I would still be all "ugh" in my thoughts (I would never voice that reaction to anyone to propositioned me, by the way)

Given the context, I disagree with your assertion that "asking isn't making assumptions." You are right that lots of men ask for a date when what they are really asking for is sex, and I generally rely on context and word cues to tell the difference (and sometimes I am indeed just up for sex), but I would prefer the two to be more separate. Certainly dating includes sex but to me it is about more than just sex, and in the case of this letter, THIRD didn't identify herself as poly or suggest she was looking to date this couple and begin a triad relationship. She thought they were both attractive, wanted them, and projected that onto their friendly reaction to her, much as any pushy man has ever done to any woman who's merely being friendly, and furthermore rolled it all up with the assumption that every straight couple is open to an MFF threeway and wouldn't they be lucky to find an "attractive and willing" unicorn like herself who lives out of state and would therefore never bother them again. Yes, to me, that's presumptuous and rests on a good many assumptions.

In particular, I would argue that it is very much making assumptions to think that a married or in any way socially partnered straight couple you meet outside an environment explicitly dedicated to facilitating dating or hookups or any other sexual activity would be interested in fucking you (universal "you") based on friendly rapport. Leaving the issue of how ubiquitous bisexuality is, the vast majority of married straight couples are monogamous (or at least one spouse believes they are).

I can't see that THIRD assumed that every straight couple is open to an MFF threeway. Indeed, her letter to me is premised on her not so assuming. She's asking for a non-offensive way of asking.

@30/nocute: "There's an attitude of entitlement and superiority in this letter that is so off-putting. I think it starts with the "unicorn" self-labeling. You don't get to decide whether or not you're a unicorn. Someone else has to make that designation."

I agree, as I've said before in previous comments. Designating yourself a "unicorn" does not make sense. The numbers of women interested in threesomes isn't so rare as to make them near mythical creatures. What made a women who are interested in threesomes with a particular couple rare were the numerous and highly-limiting criteria imposed by the couple seeking a third.

THIRD's couple by the way was described as "both very hot. UNBELIEVABLY hot." If this is a couple that wants threesomes, they won't have any difficulty finding a third for sex.

The argument goes that the popular usage change, but of course it did. Who doesn't want to be described and a rare commodity, and who wouldn't adopt that term for themselves by self-labeling. But THIRD wasn't this couple's unicorn, they don't have a unicorn problem.

@43: You're right, Harriet. I am over-reacting to some parts of her letter, perhaps. I do see that THIRD is trying to find a delicate way of asking and that she refrained for fear of looking like a jerk.
It seems to me that she's sort of asking for permission to just go ahead and make assumptions and act on them and that bugs me.

NoCute: Since you and Traffic both misinterpreted my hypothetical, let me restate it: If you were at a wedding on your own, no husband, and a single man chatted you up, would you say "ugh"?

If Harriet's right, and Harriet made exactly the same point I did, I guess I'll take that as a victory for my position, if a failure of my attempts to articulate it. Thank you, Harriet!

If THIRD was assuming the answer was gonna be "yes," she wouldn't be struggling with a way to ask!

@nocute, I have to disagree that she's being at all presumptuous. She knows that some people would be interested in what she's offering, and she's asking for the best way to check if these particular people are. That seems like the same basis for any interpersonal interaction, really, including most dating. And as for dating vs. sex--whenever I was asked out, I pretty much assumed that the guy wanted sex, and was offering to date me as a chance to get it, and that a larger relationship might develop accidentally in the process depending on our personalities. at least, that seemed true in my twenties.

If it's presumptuous to ask, then it seems like the only way to ever make a threesome happen is meeting online. I realize that's all the rage these days, but it just doesn't do it for some of us--and how the hell did people have threesome before 2000?

@46, 48: Okay. Maybe I'm just being grumpy.
I read tone as much as content, and my tone meter seems to be tuned more highly than the rest of you all's on this one or at the moment, I guess. I do value your opinions, so I am willing to concede that this is on me.

@BidDan: You have strayed too far from the letter in your hypothetical for me. The fact is that this letter is dependent on an intersectional situation of both presumed bisexuality and non-monogamy, and you are trying to liken it to a situation wherein one straight single person attempts to seduce another straight single person. My "ugh" wasn't predicated on either the need for bisexuality or the non-monogamy alone, but rather the need for both of those things to exist in order for THIRD's wish to come true--and the fact that, as she presented it, there was no reason for her to assume that either condition existed.

I know you are focusing more on the bisesxual aspect than the non-monogamy aspect, so I will say that it rankles me that when I've put together an MFM threesome for myself, I have to assure the men that there will be no sexual contact between them (unless of course, they want it), but several boyfriends I've had had wanted FFM threesomes in which what they wanted was for me to have sex with another woman at least as much as they wanted themselves to have sex with another woman or with two women at once. While I'm down with the idea of sharing a man sexually, I don't want to have any kind of sexual contact with another woman, and so far, the boyfriends I've had got off almost more on the idea of the FF aspect.

@ciods: Yes, I always assume that someone asking me out wants sex, and certainly some people offer (or used to offer) to date as a way to get it because social rules and norms said that you couldn't just ask for sex à la carte and you had to at least pretend to be interested in developing some sort of interpersonal relationship to get the sex and then sometimes, depending on the personalities and interests and desires of the people, a larger relationship would develop. But in 2017, in the era of internet dating and dating sites that allow you to specify that you are just looking for sex, and in a general relaxation of attitudes towards commitment-free sex and hookup culture, and general greater openness, I think that it's possible to be more open and truthful about the level and nature of one's interest in another.

I have had all my threesomes (all always MFM) without using the internet. Some predated the internet. In most cases, they were arranged, but one happened spontaneously. Some of them were in the context of my boyfriends and I, acting as a couple, asking a third to join us; and lately I have put my own MFM relentlessly straight--meaning there is no same-sex sexual contact between the men (though I would be totally down with that)--threesomes together by asking different FWBs if they were into the idea. Granted, I met most of those FWBs through dating websites, but then I have met my last several boyfriends through dating websites, as well. I think that as we get older and our casual contact with new people diminishes through life circumstance, the internet is how many of us date today. I think that when people are in their 20s, they probably still find their romantic and sexual partners live and in person more often.

@25 that could backfire. There's an extra-hot bi-girl in my social circle. She's unattached. She describes herself as a "unicorn" and literally dressing up as a rainbow unicorn is her goto party costume. Once, while drinking, I chatted her up about it, hoping she'd be into me and my then girlfriend. She had *zero clue* of "unicorn" meaning "bi girl who will be with hetero couples". This is a woke-ish white girl in the bay area who's like 26 years old and went to fucking Vassar and had no clue.

Nocute @49: Your experiences are leading you to read presumptuousness where it does not exist -- just as mine have led me to call for more caution than most folks might deem necessary. Your "ugh" is towards your past boyfriends; don't project it onto this letter writer. They may have "assumed" you'd be down for same-sex fun, but THIRD is doing nothing of the sort. She is not assuming that either the couple is open or that the woman is bi; but given that both may be true, I'd ask you, how will she find out unless she asks?

Sportlandia @50: Similarly, I recently saw the OKCupid ad of a bi woman who described herself as "sometimes a unicorn" (in the sense of liking to dress up as one) and then went on to adamantly state that she is sick of being approached by couples. Um.

@45. Nocutename. First off, you are thoroughly within your rights to say that, if it were you, that if you were in the situation of a wife propositioned by a third, you'd take it badly. Not that you'd be rude or act offended or afterwards come down hard on some notional husband for flirting; but that, inwardly, you wouldn't like it.

Beyond that, I do think there's some form of being GGG in contexts where we're going to decline sex, rather than take the opportunity up. A kind of manners or sexual civility, if you will. But you would be amply showing this in just saying 'no' politely.

I think she's requesting permission to ask but not to make any assumptions. And what's conceivably offensive about her assumptions, anyways?

I'm with nocute on this one. You don't approach a married couple and ask " you wanna fuck."
Isn't that what married means? As in, please respect our commitment. Why all the noise about marriage equality if not because marriage as a cultural institution is sending out a big message.
I also agree with nocute that this girl sounds very entitled. Goes to a wedding, enjoys chatting with a couple and is here asking if she should act on it , after the fact.
Did they take your mobile no, LW? Ask for your email address? If so, I can't remember the whole letter, then they showed you a clear sign they are interested in further contact. If they didn't, there's your answer.

@BiDanFan:
nocutename said "Ugh. I'm imaging that my husband and I are at a friend's wedding and we start chatting with a single woman...

And you said: "Would you "ugh" a request for a date from a single man whom you weren't interested in?" So, yeah, you probably should have clarified if you meant "but what if you weren't married."

To answer that, if my grandma had wheels, would she be a bus? Maybe, but she doesn't. The point was that it is rude and socially inappropriate to proposition a couple (or either one of the couple separately) unless they have clearly indicated they are not monogamous.

Thank you, LavaGirl and Traffic Spiral.
@Harriet, I don't know what you're talking about. I'm not advocating not using tact and polite manners, ever, neither when declining unwanted sex or at any other time, and I don't see how my thinking that the woman is pushy and entitled and presumptuous makes me "take it badly." I also really don't know how you'd assume that a typical wife's reaction to the situation of a single woman mostly chatting her up (read the letter again--THIRD hit it off especially with the wife) who would then proposition the couple would be to "afterwards come down hard on some notional husband for flirting."

@nocute, I could be wrong, but my reading of Harriet's post was that he was acknowledging that you would be polite and tactful, despite not being pleased about it.

@56. Ciods. Correct, thank you. I said to nocutename that if someone hit up on you and you weren't interested, you would be 'within your rights' to take it badly. It wouldn't be bad manners. It wouldn't violate an intimacy. It would be OK for you to recoil inside. So might I. So might anyone. But hopefully we (nocutename and I) would express our dismay in a moderate and polite way, just by saying 'no'. I find it hard to see how my post could be read otherwise.

@54. Traffic Spiral. Sentences like yours beginning 'the point was that it is rude...' to me underlie the theory of gender separateness and all its travails (and unhappy real-world consequences). I don't agree with it at all.