Profag

Used in online games to describe a player that thinks they are a pro, but in reality they are just a fag. Mainly for First person shooter games, all players that whinge every time they are killed, if they lag, if they think someone is hacking but they aren't, etc.

Any professional gamer that's way too good at a video game.

Usually they know that they are good and are complete assholes about it. Also if you are playing with them they'll get mad at you for doing something wrong on the game.