(HIGHLY ANTICIPATED THEATER) The Pillowman (the Martin McDonagh play about a writer, a totalitarian state, vicious cops, and a grisly string of child murders) is already ruining relationships. Five of my friends saw it in New York and said it was "killer," while two others went to a museum. The two who went to the museum are irritated that the others won't stop talking about The Pillowman. Don't make their mistake. Today is the pay-what-you-can preview. Get there early. (ACT Theatre, 700 Union St, 292-7676. 7:30 pm.)