How do i make him stop??

well there is this guy that really likes me...we are in the same l.a. cl and he always stares at me. he asks me out at least once every 3 weeks or so and it is starting to annoy me!! it has been going on for a year now and at first i felt bad for telling him no but now i am uuber mad!!! what should i do to get him to stop?? whenever he talks to me he also get very suggestive and he is really immature and obnoxious!