A guy that is my friend likes to touch the top of my head when I am sitting down and he is standing next to me (I have a short buzz haircut). He either rubs top of my head or he taps it lightly with his hand like a drum. He did slap me behind the head once when I said something stupid... I am actually getting annoyed by this and I am not sure if he is doing this to make some kind of statement. Does anyone do this and how do I deal with this mannerly?