It really all depends on the circumstances and how they are being mean. If they're shouting at you and hitting you they are usually frustrated about something. This could be anything from failing exams to personal or family matters. If they're ignoring you they may just want to talk to someone, maybe you, but they just don't know how to get the words out. If they're trying to make you jealous, well, that usually means that they like you. That makes no sense, but that's a girl for you :P
deepanshu_gandhi