If I like a boy, I will pretend to look down on him and be more reserved! What should I do if I’m too tired? Tell him how embarrassing it would be if he looked down on me?

There is something wrong with your mentality. Since you like him, there is no need to pretend to look down on him. It is okay to be reserved but you must also pay attention to politeness. In fact, if you like him, you can test it out, have more contact with him and communicate more, and see how he feels about you. If you think there is a chance, then the two of you can make it clear. No matter whether it succeeds or not, you have at least tried hard.