god moder
A roleplayer that will do what he wants despite resistance from the Dungeon Master or the other players.  Generally a nuisance and usually a munchkin.  Term taken from the common "God mode" in various first-person shooters that renders you invincible.
Gary is a God moder.  If you say the world explodes, he'll say he goes Super Saiyan and makes a shield to protect himself.