Okay the rule is you CAN kill someone for following you. Nothing says you have to so stop complaining. If he is willing to give up his round because he wants to follow some one that is his fun. It is your paranoia that causes your karma to drop. However this is a good example of a reason not to ban for low karma.
He's followed me around quite a bit. You know how I solved it? Discombob, door spam, or teleporting. Solved the problem without rdm.
As for the real rdm, it should be punished accordingly.