Phoenix, AZ is the road rage capital. About once a year there is a story about a driver firing a pistol at the car in front of him -- just because it got in front of him. One pushy lady followed me into a parking lot and called the cops because my car got in front of hers.
Another thing I noticed about once a year is when I am driving along in the left lane and a car is following me. After a while I need to be in the right lane. Now the guy behind me decides he needs to be in front of me, and he thinks he can change lanes and pass faster than I can change lanes. When he can't do it (because there's a curb over there) he honks the horn as if I did something wrong.