Most of the things people get pissed when playing online are:

-People complaining when they are down and there is a large amount of zombies around, ok let me freeze all the zombies and revive you stupid P O S
-When the host ends a game because he-she wasn't revived
-People who get in the way when your running a rape train
-People who talk sheet and can't back it up
-People who play music on their mic
-People who stay by you the whole game like "hold my hand" players piss me off
-LAG

Heres a small list anyone lese have something different they would like to add ?