Gay Best Friend. When a guy and a girl are extremely close friends and the guy puts her above all his friends even though they are in no way going out. For example, if the guy is with the girl and passes two friends hanging out on the street, he will completely ignore these friends and just keep talking to the girl.
Friend 1: Hey look it's Korman, is he coming over to say hi?
Friend 2: nah, he's to busy GBF'ing to talk to us