Hi!
First of all, I want to tell you I admire you for being so strong to go through this annoying situation for so long without your parents doing something about it. You are only 15 and should not be subjected to this torment from an older brother of 19. Your brother is crying out for help of some kind. He is lonely and bored besides pesty. He should have more hobbies and friends and because he doesn't, you are his target. Doesn't your Dad do anything about this? Is there a close relative you can talk to who can talk to your mother? How about telling a school counselor who might then call your parents and tell them to get on the ball? Your brother sounds troubled and you can try to be his friend as someone suggested, (maybe teach him the guitar or play ball together?), but you are not his psychologist. When I was young and my brothers and sister bothered me (it is somewhat normal in families to have this happen to some degree), I went over my friends' houses for peace of mind. Don't do anything to your brother you may regret. I think you first need to call both of your parents together for an emergency meeting and tell them just how you are feeling and that you need your privacy and peace from this big pest. In the meantime, believe it or not, sometimes ignoring or laughing with the person might make him go away. He is getting a reaction out of you that satisfies him. When he sings, sing along with him, lol. Be creative. think outside the box, but don't let him see he annoys you. You are definately the stronger one. Yet, still get the outside help you need to cope with him until your parents act on this. Let me know how things are going, will you? We'll think of something that works after trial and error. Good luck. Don't let him become your obsession as he wants to be.