Have you ever flipped the bird to someone else? Did it get you in trouble, or did it make you feel better?
Rude behavior can take on many forms, which also includes flipping the bird. Some would say that most everyone has at least once done it, or thought about expressing themselves in this fashion.
We recommend you think first before over reacting. Mind your manners and try to be extra polite. Some say it makes them feel comfortable and allows them to blow off steam.