What do you do if a girl knows you like her and then she ignores and avoids you then stares at you a little but whenever you talk to her she seems deadly serious and bored?

The reason she acts that way is because girls aren't as obvious as boys about who they like. She might think you are cute, but not a good person. She might just be looking at you and wondering why you like her. Or, she just is with her friends whenever you are around, so she wants to be with them instead of you, but she still might like you. Maybe she's embarrassed that you like her, or maybe she thinks that by acting this way, you will like her. Playing 'hard to get' often ruins any possible relationships.