winjoin
A verb meaning to purposely join the winning side in a team vs. team video game match. It's usually done by a scrub who wants to make sure the better players are on his or her own team.
You fuckin noob! Why do you always come in here and winjoin and then you ragequit if you can't?!
winjoiner
In eg. Quake 3 Arena a person who joins the other team even though their score is much higher and are likely to win is called a winjoiner. A winjoiner is not very well seen by other players.
WTF?! Egghead winjoiner! Kick him!