Acronym for Faggot Against Gays. It is a term used for closeted homosexuals who try to prove that they are a heterosexual.
John: Oy my God, you are such a fag Bill.
Bill (Gay): At least I'm not a F.A.G.!
John: I'm not Gay!!! Shut up, SHUT UP!!! (John goes away crying and running like a girl.)