Longer answer: It might be because he likes you, and usually due to at least one of the following:
They're awkward about it (given that you're under 18, I'm assuming he is, as well), and don't really know what to do about it. Not knowing what to do, or being afraid of just asking you out, he's chosen to annoy you instead. Presumably, this is in the hopes that he'll figure out what to do later, or become comfortable around you to the point that he can just tell you he's interested.
They really haven't realized that they like you (boys can be very dense), and are just harassing you because they like being around you for some reason, and have decided that it's fun to pester you.
If you give him a bit of time, he may come clean (one way or another), or you could go the direct route and just ask him if he likes you.
Hell yeah when you don't have game that's the only thing you know how to do so far. Because if you can get someone excited or mad at you that shows you like them and care what they think which gives them attention from you, and their immaturity tells them to bother someone to get their attention. What I would do is call him out next time he does that. Say why you doing that? Is it because you like me? Ya know you could just say hey your cute or I like you it would be easier and less irritating. You will shock him but hell respond. And that should get him to stop acting foolish and communicate better. Sometimes you gotta be a little ballsy to people ya know? Good?