I've teabagged people, but that's hilarious (honestly, I've nearly been in tears before whilst doing it, I find it that funny), not rude.
Once on CSS though, I challenged a guy to a knife fight since we were the last two in a round, but when I dropped my gun I did it in the air so that I could catch it again and shoot him. I think that's basically a war crime in CSS.
I don't think I've ever been abusive to anyone. Apart from the aforementioned sex and war crimes, obviously.
Ooooh, no! I've forgotten my finest hour! On Left 4 Dead 2 I'd gotten majorly fucked up at the start of the last campaign, so was low on health, and my other team mates had all healed and picked up the safe house medpacks too. I must have asked 5 times for someone to heal, but no one did, so I waited for one to run out of the door, he got caught out by zombies, and then I shot the other two in the back whilst he was getting fucked. All 3 were down, I teabagged the living shit out of the ones I'd shot in the safehouse (tee-hee), and then I disconnected before they could all vote to kick me.
Its called co-op for a reason, bitches.