Why do other drivers seem to go mad when you have to use your horn to warn them of your presence?

I know what you mean, haha I think that they get embarred and need to find some way to defend themselves so they give you the finger or act all ticked off. What I cant stand is when your driving down a two way street and the person coming towards you will hug the side of the road because they have a fancy car and they think youll hit it or something