At least in WoW they do when they think they are the stronger one. When I played WoW, I played a lot of PvP and because of that was obviously better (not saying I was good, just that average player plays barely any PvP, even on PvP servers) than average player on it. I didn't attack people when I was leveling, I got my PvP fix from arena and battlegrounds, but really often people who were a bit, not much but just few levels higher than me constantly attacked me probably thinking they get easy kill. I can guarantee you most of them were mainly PvE players seeing most of their attempts to kill me weren't that good and what they did was basically just CC to PvE rotation. If after first death they come attacking me again, I will just kill them every time they are in sight, and according to amount of whispers from their other characters, I'm the one being dickhead when I basically just defend myself. Most fun was when they came in with their max level characters to show me who's the boss, I always had my main close to my leveling location for that reason, so now they just keep dying with another character.