It costs nothing to be polite. I've always believed that how you conduct yourself is a reflection of your self-esteem. When you go out of your way to be nasty to people, it says a lot. Lack of control over your life maybe, so you attempt to exert power over other people to feel better? Who knows? Why take out your frustrations on strangers? If somebody does something dumb that I can't stand, I just leave. I don't feel the need to heckle them.