Mr Shrike said:
Sometimes I do it as revenge for being teabagged myself, as it's just the ultimate "You will never beat me" statement.
Or occasionally when I knife someone from behind on BF:2.
I'm in a somewhat similar mindset. However, I do it to people that hack or cheat instead. Or, to those that are being epic assholes in game, either to someone in particular or to everyone.
Case in point. Some friends of mine and I were playing a game of Left 4 Dead 2. We started a lobby and waited for it to fill. Before long, we had 4 other players and started up the game. Literally as soon as the game began, the other team vote kicked someone. I had a sneaking suspicion, so I checked the gamercard of the three left and the gamercard of the player that joined immediately after the vote passed. As I had suspected, they were a Gamebattles team that pretended to be pubbers. And, instead of asking the other player to leave, they just booted and brought in their friend.
Anyway, as the game progressed, things got out of hand. They were good players, no doubt, but they weren't THAT good. The only advantages they had were the exploits they kept using. For example, the shortcut on Swamp Fever - Chapter 4, that let's the survivors skip the catwalk crescendo. (before it was patched)
They were ahead in points, so they were survivors first on the level. Naturally, being the kind of dicks that they were, they made a B-line right to that little shortcut. We managed to kill two before they got to the saferoom, but that didn't stop them from teabagging our killed infected.
When it was our turn, we decided to play fair and actually do the crescendo. Unlike our opposing team, we all made it to the safe room. Just before getting there, though, the other team tried one last group attack to get some downs in. After we killed all four of them , we all picked one of the corpses and tea-bagged simultaneously. To no ones surprise, they all rage-quit on the spot.
Was it a dick move on our part? No question. Was it worth it? You're God damn right it was.