As a priest in WoW there were several fun ways to utilize Mind Control to poke fun at other players, but honestly it's a bit too obvious. My preferred way of killing an enemy player is using a rogue's Distract ability to change the direction someone is riding in, preferably when they're riding next to a cliff. A slight adjustment of the angle, and they won't even know what happened. Camping around stealthed next to the Hellfire Ramparts before players could get flying mounts at level 60 was a particular favourite of mine.
Not really weird, but definitely funny. For me.
I don't really play any online FPS's, which I assume is where most "weird kills" would happen, but I once by mistake threw my sidearm at someone in CS 1.5, who then mistook it for a grenade seeing as things happened so fast, and jumped off a building to avoid the said grenade. It was at a LAN, and we both sucked, but it generated a fair bit of laughter.