I want to do a Harry Potter room, but I'm worried my friends will tease me, as I'm nearly 14. What should I do?

If your friends tease you because you are into Harry Potter, they are not good friends. I know many people who are in high school and college who love Harry Potter and would love a room like that. It is your room, not your friends', so you have the right to decorate it to suit your personality. That said, consider to what extent you will decorate, and ask yourself (and your parents, trust me they probably know you pretty well, even if you don't want to admit it) if this is a room that you will like by the time you are a senior in high school. This has nothing to do with what is "cool," but your own personal interests.