Why the hell is he so mean?

I don't understand this new guy comes to school flirts with everything with a pulse and he is really mean to me always calling me slutaway instead of hathaway I mean I don't mean to pry but I know I'm quite pretty I'm not a barbie doll or anything but I'm not bad im always nice to everyone and the only thing I said to him befor this behavior is hi I don't get it help ?