Reign: Just say no. You're not obligated to go with him so he'll understand. There's no way to let him down easier than to blatantly tell him that you're not up for it, because in the end he'll face rejection anyway.
Anna: You have to realize why you don't like him. If it's really shallow and all, that's a really bad reason to not go out with him. I mean you never know because, how well do you know the guy? You really have to consider his attitude and how he's asking you. If he's persistent and it's really annoying, find out why and if his answer is too shallow then hell no. But if you really don't want to, sit down and use your most gentle voice and tell him no. Asking other people who know you and him personally to help you say no may be good too.
"My teacher doesn't like me and I feel like he's failing me on purpose. What should I do about it?"
Reign: Well it's rare for a teacher to show that much favoritism, but instead of assuming that he's failing you on purpose, just prove to him that you are smarter and you deserve a better grade than what he's giving you. Forget about it and just start studying more. You make the grades, teachers are just there to compute them.
Anna: Talk to him. It may be really hard and it is your grade after all and if you never stand up for it, the problem may never be solved. It his reasons are too shallow, go straight to the year lever coordinator, or whoever is in charge.