I agree with being able to defend yourself against tkers. The current rule that you have to let tkers kill you every round over and over again without fighting back is absolutely ridiculous. Let's face it, in real life you wouldn't let someone hit you to death, so why let it happen over a video game?
Unfortunately, too many idiots will mistake an accidental FF hit as intentional and TK his teammate - which just snowballs from there.
So instead of Tking him, go fight the enemy. If he follows you with the intent of purposely injuring you - get an admin's attention. If there aren't any online, make a poll. If the polls are off, take a screenshot and post in on the forums.
You may take the risk of TKing the guy, but just know that we will not be wasting our time trying to figure out who started it. You'll both be removed.
Also, you might want to brush up on your reputation in-game... in tends to help not attracting negative sentiment from teammates.