Bad jedi that don't get better and are on your team.
Bad gunners that hide rather than engange the enemy. Not even talking about snipers, there it's justified somewhat, but cr3 users?
Rocket Arcs that don't know when to rocket, how to rocket, just rocket only for the predictable pushback.
Idiots that pause to say sorry in the middle of a firefight for tking you. You want absolution? Finish the fight and then say srry. Tking and then getting killed because u paused to chat to type srry - reaffirms your stupidity.
Bad class players. There comes a point where you want to shout, change your class stupid, you've played and sucked long enough as the one you've been playing for god knows how long.
As ever, teams. Be it numbers or skill stack. Forget numbers or skill stack actually, the worst stack is the noob stack. A team stacked so full of noobs that afk players have a greater chance of defeating the enemy.
Idiot players that let flanks happen, they just sit and watch only to die pathetically near the end of the round because the entire team got rolled while they sat back only for their brief fart out of existence.
Nothing so frustrating as being on a populated server full of *special* players.