OP, he's just trying to either assert dominance or at least find out if you are on equal grounds. With all the nonsense of how to be more alpha talk around here, I'm surprised at some of the suggestions being given. Guess what? You want to be alpha, this is how it's done. No one ever acquired said status without confrontation and living in their comfort zone. He may just be busting balls. Bust balls back. He obviously sees something in you enough to test. Invite him and some other co workers to go drink a beer and see what he's about. Y'all will either find common ground or you'll see he's a genuine fvcktard. In the latter, punk his a$$ out. Preferably, in front of the rest of your coworkers.