A WAR did it to me once already in Seize after a 3v1- don't really see much of it though, but I generally don't die often.

For him though, I hope it was worth it, because I made sure to mark whoever was healing him, and then the minute his support was dead, I'd mark him. He never got away.
The only thing I would want to say to him is "I hope you enjoyed that 1/4 record, buddy! Thanks for the 15 points." Just a shame we didn't win that game. 797 points or something like that.

I have witnessed some karma kills though- some SMN dancing on top of one of our tanks after killing him and laughing, only for me to come around a corner and plunge+stun them while a MNK charged in on them and LB'd.

The most I've really done is /beckon to some people in 24 man games in an attempt to pull them away from their group for a 1v1 or 2v1.
Works great most of the time on randoms in Secure when defending our cap, but its not really viable or practical to do in 72's.