I can only remember one time where I was full-on griefing other players... Normally I'm a good boy who likes being complimented for his good done to others, and not bad.
It was a custom game for WC III, widely popular, and was basically a sort of team-based tower defense where you can spend your gold on workers to gain additional income or on towers to suppress the waves of enemies more fluently.
Now, I had little to no clue how to play this game, as my brother was the only one playing. So, as I had absolutely no respect for the game, and my brother asked me to 'take over' whilst he had to do something else... The griefing began.
It was quite early on, so players were only just establishing their economy and towers and such. And me? Well, I just wanted to sit down by the cork-tree and smell the flowers... Mmmmm.
And of course, since it was a widely popular game, and these people had maybe played 100-200 games outright making it serious business, one of my mates picked up on me slacking off. He CAPS-LOCKED obscenities at me and called me, or actually my brother, a noob and such. Very, very vulgar was he, and very very mad. I just replied with the most retarded shit imaginable at all times with not a care in the world.
And so, the !votekicking began (!votekick Playername is a command you could issue and it would create a democratic way of getting a certain player out of the game). He was quick to issue it after I called him a turd you had to flush twice. BUT ALAS! I was surprisingly not vetoed out of the game! The votes of !yes were highly lacking, not enough to support my dumb ass to being kicked out of the game. Shortly thereafter, my brother returned and found himself the prime object of hatred from his one peer, as the others didn't give too much of a shit.