How do I handle this with my bf? He makes jokes that hurt my feelings?

Both 17 and dating a year. My bf will make sexist jokes and jokes about my intelligence level. I have told him that I don't like these jokes and they hurt my feelings but he'll just makes excuses like "I don't know what I'm saying half the time" or something like it. It's so annoying. For the smarts jokes, it could range from him starting to say something and then stop and say "lemme say it in a way that you'll understand" and he'll say it sarcastically. Or he knows I'm taking an AP class next year, and when I told him about it he said "are you sure you're up for that? It's gonna be a biiiiig challenge for you" and then he patted my head. It makes me feel worthless (and I've told him this). He says it's ok For him to say those things just because he says "just kidding" afterword. How can I get him to stop?