I'm level 43 atm, and I've come to kill players often when online. Wasn't always that way, but its pretty much all I do when I play now.
When I feel like havin a good ol' free roam deathmatch (which is often) I usually, but not always try to provoke players to shoot first (i.e drive slowly by them to see if they attack). That way I feel less guilty about griefing them in the end. Sometimes I go rooftop sniping large groups of players, annoying people on mic, and low levels with Adders or Xfinitys. I also like to hunt players with very high levels. Noobs who use tanks, I keep an eye on 'em, and as soon as they get out or eventually explode, I have my way with them.
In the end, I don't randomly kill people. I pick my targets.