When a server has clearly posted rules and someone's violating them, I point out the offender's sad counter-social behavior by chat—politely, twice.
If the behavior continues (it always continues) I get the irresistible urge to tattle, hoping somebody will kick the putz.
What's the best way to contact admins? General chat? I've read that some servers (BC2CC?) support chat-based directives like !admins and !calladmin, but I've never gotten them to work. Maybe I'm doing it wrong. Can I tell whether I'm on a server that supports them?