As I can see Zundfolge said, there may be a TK limit. Somebody else said this was off on that particular server (this is good, the entire team can target him right away and eliminate him from the game, he will be dead before he can do it to anybody else.)
If the TK limit IS on, find a way to divide the killing of him. Zundfolge says the default is five, so each person can kill him a total of four times without repercussions. If an order is devised, this killing of him can be extended as long as possible without anybody getting kicked and having to rejoin. For example, in a 6x6 game, he will be one out the six, with the other five able to kill him four times, for a total of 20 times, without any of them being kicked. Trust me. After 20 rounds, he'll get tired of being dosed up with his own filth and not having a chance to get back at anybody. By the time the first person gets kicked on the 21st round, he'll be out. Everybody will be kicked and have rejoined and have the slate wiped clean by the 26th round (since the last person in the order would get their fifth TK on the 25th round,) etc., etc. 5x6 isn't so bad. Furthermore, the players can also (through team work) explain to any inquiring administrator what happened and justify it that if five of them are ganging up one guy, that one guy is a TK'er, and instead of having legitimate players TK'ed, the only person TK'd is the original TK'er himself. Since somebody WILL be TK'd every round, and probably multiple people if its the TK'er himself doing it, the best solution is to have only one person TK'd, that person being the original TK'er.
By the way, when making the demo, it would be most advisable to force himself to admit he's TK'ing you just because, so he can't use the excuse "they're a clan and don't want me playing on their team" or whatever lies he'd spout. By using clever verbal baiting, he'll say "i'm tk'ing you cause you're a fag" or whatever, and then ask why you're a fag or whatever he said, and say things like "we never TK'd you" (make sure its we and not I so that he can't say others were TK'ing him) sooner or later he'll admit to this, and youll have it logged in the demo, so any suspicious admin will clearly be able to see that it was he in fact that started it.
Again, I never, <i>ever</i> condone banning. EVER. Try this instead. Its like a chess game. In a chess game, each player has a the same amount of pieces, and its up to one to outsmart the other at his own game. And it always works, every time. Just be smarter than him. A Tk'er can't be that smart anyways.