Previously unknown person who sneaks in and takes the girl/guy who has recently become available and that you've wanted for years; typically about ten seconds before you're about to make your move.
Who's that crapweasel and why is she making out with him?
Person who thinks that they're really good at playing Unreal Tournament, but who in reality totally suck ass and drive your stats into the ground when they play on your computer.
I was ranked number 15 until I let asspigeon play. Now I'm number 198445.