My guy friend likes to pick on me?

In my group of friends I have a guy friend who is constantly touching my lower back and sides and trying to tickle me or poke me when we all hang out. He will come up from behind me and pick me up and carry me around to joke with me. He doesn't do it to any of the other girls in our group of friends and tells everyone how much he loves to bug me and pick on me. We are both 19 and I know he is openly dating people, so why does he do this to me? Do guys normally do this with their gal friends?