Acronym for "gay after beer". Commonly seen among college frat boys who think and act like they're totally straight, yet engage in various homosexual acts once intoxicated.
Guy A: "Dude, that new pledge is so hot...I'd do anything to suck his dick. I wonder if he has a girlfriend"
Guy B: "Oh please...he's a total Gab
...just give him a few drinks and he'll be on his knees in no time."