I think I can top these as far as pure evil goes. Mine goes back to the old days before the internet, where we'd play multiplayer games on BBS's. It was a space game called "Tradewars" where you had a certain amount of moves (1 move per tile on a grid) and then had to wait until the next day to continue. You'd normally have up to 200 moves, but if you died, you'd be limited to 50 so you could escape.
I was aligned evil (of course) and was a member of a 5 man Corporate (team). The #1 player was aligned good and had incredible weaponry on his ship. Normal ships in this game would auto retreat if attacked. This guy had an auto attack system and we had a scuffle above his planet.
Mine was the most powerful "pirate" ship, but it was no match for his, even though he was unattended. I couldn't win the battle toe to toe, but I stayed in the fight and mined his planetary system with every mine I had before he destroyed my ship. My mines had damaged his ship, but he was still alive.
I was in an escape pod and still had turns left, so I went back to my Corporate's planet and borrowed a teammate's freighter. I borrowed every mine my teammates had and went back to the "good" planet, dropped the mines and went back home, leaving a message for my teammates before logging off.
Later that night, he logged on and immediately blew up, having activated the mines. His logs showed me losing the fight and then returning, so he accused me of cheating, but I had no way of cheating and wouldn't if I could. It was a pretty funny message that he sent and he posted it publicly so everyone could read it. We had a good laugh.
The evil part of this is that I not only didn't gain from his destruction, it cost me turns that I could have used to rebuild myself. I also could have retreated when we first met and would have survived with my pirate ship intact. So I did myself "harm" by causing his demise.
It was so worth it.