Why do people LAUGH at me in public?

Teenagers are mean to someone at some point in their life no matter whether they think anything of it or not, it could be for any reason from what you were doing to the look on your face. I'm 15 too and it happens to me occasionally and I also do it to other people. I just wait for the day we all grow up and realize the people we taunt today could be the ones signing our paycheck tomorrow.