I know that the other player was provoking you and he had tked other people, but teamkilling is still against the rules even if you think it's justified. DTV is about teamplay, and a teamkill only makes it harder for the team to win.
The next time something like this happens, wait for the start of a round or wave, write the reason for a ban-poll and then make the poll (or just report his teamhits).