I've perfected a new form of griefing in Day of Defeat: Source. When I'm not messing with the poor God-fearing boy scouts on the Christian DoD:S servers, I like to find new and interesting ways of teamkilling without getting punished. My new favorite method is the reverse teamkill.
It works like this: Join a server and choose a player with a reasonably high score to pick on. Hit ~ to bring up the console and type name Player , where "Player" is the player's name. The trick here is to add a non-breaking space at the end by holding Alt and typing "0160" on your number pad. Nobody will notice the extra space.
Play it straight for a few minutes. Rack up five kills or so and try to capture an objective or two. Then start punching your teammates. Be careful, though: you only want to hurt them, not kill them. Don't be too obvious about it, but don't worry if they catch you at it. Your goal is to get them angry enough that they start hitting back.
Before long, team chat will be rife with messages like "Player is team-hurting!" and "No I'm not! That's not me!" and "Ban Player!" Resist the urge to chime in. You want to be completely silent. Let the tension build.
Most servers have a revenge menu that you can use to punish people when they teamkill you. Use it! Once you've pissed people off so much that they start shooting you, the revenge menu is like a get out of jail free card. You can use it to kill your teammates, and the best part is that they get double negative points! Meanwhile, keep killing enemies to keep your own score up.
If there are admins around, you'll probably get kicked eventually. No worries, just move on to another server. If there aren't any admins, then someone will eventually call a vote to ban you. This is where things get really fun. The voteban menu on most servers lists players by name, and there's absolutely no way of distinguishing between "Player" and "Player ". Half the people who vote will probably vote for the other guy, leaving you in the clear. This will cause all sorts of exciting chatter as the original Player realizes he's being framed.
If you're really, really good at this, you can finish the round as the only player on your team with a positive score. And if that's not a worthwhile way of spending a Saturday afternoon, I don't know what is.