How is teamkilling penalized in BF3?
There is an anti-team-killing setup on the server side of things. Server admins can adjust these as they see fit, but if you team kill enough you'll get booted.
This is what the defaults look like:
There is a server side setting that causes you to be kicked from the server after a certain amount of team kills. This is obviously decided by the server owner, so some servers will have it set very low (maybe even 1 if they're extremely picky) while some will give you lots of freedom (maybe set it to 50?)
There is no anti-TK system in the game itself, but I expect this to come in a future update.
We all do.. gives the MW3 fraction a leering look