1. after a certain amount of teamkills, the teamkiller gets automatically banned. To view this amount, open your console with the key under ESC and type in g_tk_limit
2. you can always contact the admin
3. Switch the team
4. get on servers that are well-administrated
5. There might be a server mod running, which supports kicking/banning
try to type into chat !vote kick playername or /vote kick playername. If it worked, type in /yes or !yes to cast your vote.