In Humpday, a pair of thirtysomething, heterosexual male friends decide to have sex on camera and submit the results to The Stranger's amateur-porn competition. From this ridiculous premise, writer/director Lynn Shelton spins a small miracle: a deep, hilarious, completely contemporary relationship comedy that explores with almost scientific precision how such a ridiculous premise would play out in real life. The results—executed by an ace cast led by the singularly appealing Mark Duplass—will have you squirming and howling. (If you can't make tonight's gala screening, there's a regular screening on Sunday afternoon.) (Egyptian, 801 E Pine St, thestranger.com/siff. 7 pm, $13–$25.)