I don't really do anything super dickish. The closest is probably when I got super good with grenades in the original Team Fortress. For me it made the difference between winning and losing. An imaginative scumbag with decent aim could land one of those little bastards just about anywhere at the exact moment the enemy entered that space. I used to get cursed pretty often.
I've occasionally gotten frustrated with the stealth sequences in Black Flag and just straight-up murdered every last guard in the area, whether they were actually in the way or not. Killing fifty men to overhear a conversation seems pretty callous but, on the other hand, the game is basically about murdering people in creatively underhanded ways.