I've been acting like a sociopath toward a friend since October as a Halloween prank.
Why do you act like a sociapath?
It seemed so funny to do, I have been laughing out loud when I have been doing it.
As long as your friend is fine with it for now, then there is no problem. It is Halloween after all.
Well, I kind of miss the jokes but it has gotten boring. I will stop by the end of this week.
That sounds like a good idea.  Even fun pranks can go overboard, and you don't want that to happen.  However, I have to stress that you should let your friend know that it was all a prank, and that it is definitely over now, because you don't want him to suspect anything about you.