Girl Using Y-chromosome. A guy that's actually a girl in real life. Used in MMORPGs, online avatars and the like. Compare to G.I.R.L., which is a guy in real life.
Person1: You know, that dude over there is really friendly with your in-game GF, yet he's wearing all that frilly stuff? I wonder if he's gay or something.
Person2: Woah, relax, I actually know that person; that's not a dude, that's a G.U.Y. She took that character from her brother a long time ago and decided to make it her own.