Here is my idea:
An anti-drive-by system. Even reported to online admins, even get warned, even get kicked, they don't stop. I believe that must of then even don't know what drive-by is... Tragic!TRAGIC!
Second, an anti-teamkill system. You happily ehe playing with your team, and in the middle of a war, by a mistake, you kill then :S annoying, hum? But the truly mean of this system is because there lots of players that simply don't care about who is your team, SHOOT EVERYBODY! Also will be another reason cheked of the list to warn and kick.
Well is that it.