Why will this guy not stop bothering me?

There is a boy in my Physics cl who annoys me every chance he gets when he sees me. It started last year when he tried fake-flirting with me, and I eventually retaliated (verbally). After I humiliated him in front of his friends he stopped bothering me for awhile, but now he's back at it and keeps on telling me snide things like my socks are cute and I look pretty and how am I today, all in jest I believe. I've told my teacher about it and she just made us apoloize to each other which solved nothing as the guy insists he isn't making fun of me but of course he is! And on Friday he did something terrible: he asked me to prom, in jest of course. What kind of heartless lowlife fake-asks a girl to prom?! I just walked away from him quickly but now I have to face him on Monday. How can I get him to leave me alone once and for all?