I can totally relate to you. I, too, have asked such a question as how to stop liking someone. It is not good to hate other people, but sometimes it is necessary. There are some people that you would rather forget all about.
Start by giving yourself time to be sad. If you are getting over a bad relationship, or recovering from a rejection, you need time to heal. Focus on yourself and the things you like.
Too many people, especially females, put the needs of others before their own. If you want to stop liking someone, forget all about that person’s needs and desires. Focus on the goals that you want to achieve in life. Focus on the indulgences that make you happy at the moment. Eventually, you will care less about that other person when you think about yourself first.