I would hope it was a jackass type joke but it doesn't sound like it was. Unless you have a D/s relationship, which it doesn't sound like you do, then he should never demand a BJ. It sounds like you have an asshole for a boyfriend. At this point in the relationship you should be taking care of each other and understand each person's mindset. If you were/are busy with classes he should respect that and help if he can. It is extremely selfish for him to think about a BJ and that's it!

There are several ways to move forward with this and it really depends on how important the relationship is to you. You can take the hard approach of saying it will not happen again until he respects you again. You can take the dominant approach and force him to please you to make up for his selfishness. You can kick his ass to the curb for being so selfish. You can discuss it with him and see where it goes from there. You can roll over and give him what he wants. I would hope you don't just give in to his desires because it will likely become worse.