Why Isn't He Being Sincere?

So there's this guy at my school. He's a man whore. He knows I don't like him. I told him that he was a man whore. Then he started laughing at me. He asked me if I was Obama's daughter, and sarcastically said he liked my clothes one day. But when he said it, he was smirking. Not only that, but he started to say "hi" to me everytime he saw me. So I decided to play his game. One day I told him that I liked his shirt. that it was nice. He looked at me like I was stupid and said: "Uhhh... thanks?" Then today he sat at my table with my friends. Right next to me. Even though he knows I don't like him. I was talking to someone else when he called my name. So I looked at me. And when I did, he said: "You look very nice today." He said it to me with ought laughing or smiling. Like he really meant it. But I knew he didn't. So I just said: "Thanks!" It's not like he really has any reasons to make fun of me. I'm known to have the best clothes in school, really pretty, and have lots of friends. Why is he trying to bring me down and make fun of me? Becuase if he's trying to fool me into thinking that he's being sincere, it's not working! What should I do?