I sometimes despise one of my best friends.
What about them makes you despise them?
I feel like they've become too demanding.
Friends aren't always going to get along perfectly, but you shouldn't have hatred toward a friend. Having hatred for someone will just make feel bad and will likely harm the friendship. You should talk to your friend about how you're feeling so you two can work this out.
I'm going to make them feel the way I do.
If you feel they're treating you poorly the last thing you should do is take revenge by treating them poorly as well.  If you want to preserve the friendship, the best course of action is to talk to them about why you feel the way you do!