A very smart person. We think. The smart person thonks.
person 1: *says something smart*
person 2: dam, he's thonking while i was thinking.
A way of saying that someone is being stupid.
Usually this doesn't mean that they want the other to actually kill themself, just to say they are being stupid.
Person 1: Justin Bieber is amazing!!!!!
Person 2: Kill Yourself.....