camper
Derogatory term used for someone who can actually master the team aspect fo most games, but has no one else to use this aspect with.  "Campers" generally are seen in FPS games, especially ones based on a team mindset.  These campers normally defend an objective, or wait for a tactical advantage.
OMG, he shot me in the back!  Camper!!!

You're defending the objective?  Go kill someone, camper!