Why does he act like this with me?

My M coworker, always jokes around with me at work. He will mock me, copy my voice or what I say, he will tease me about my interests. He also will come up from behind me and poke my shoulder and walk away or he will come up behind me and pull my hair or kick my leg. When I’m on lunch in my car, he will come up to my window and knock and start laughing. Is this lowkey flirting? My coworkers think so. The problem is, he has a girlfriend. I do like him though is the thing.
Why does he act like this with me?
Post Opinion