I never really noticed it, but many people are both impatient and rather rude when they drive.
I've been teaching my wife to drive (a short but uninteresting story)and it has been...an...interesting venture... Since she is just learning, she is very careful and takes her time on turns and changing lanes, etc. So, like a good instructor, I teach her the proper driving etiquettes of using turn signals and adhering to right-of-way of other drivers.
That said, I swear that half of the time, people ignore her signaling - even with a student driver sign in the window! People routinely will not give her space to change lanes when she signals. There was even one time when she had signaled to turn left into our house's driveway, some nimrod actually passed her on the left side! If she had been faster in her turning, the other vehicle would have had crashed into her/us. Then there was the person that beeped her horn at us for daring to make her 2 seconds late in her getting home (wife took a turn slow causing a delay in someone behind us pulling into their driveway).
I really wish I sometimes I was a plain clothes cop. There are a few people I'd pull over to have a chat with.