Perhaps I don't not leave my house often enough to get overwhelmed with personal experiences of other people acting stupidly, for I cannot recall any specific incident in which I shook my head at someone else's seeming lack of common sense. However, my sister has many anecdotes of crazy drivers.
One of her favourite stories is how almost every time she goes through a particular traffic circle in a giant, unmissable 15-passenger van, some other driver almost plows right into her because he wasn't looking where he was going.
My father has countless stories of silly drivers and car troubles, but only one happened while I was in the car with him. He was driving down a big highway when a lady in a white Lexus didn't look where she was going, and sideswiped our little red car. Fortunately for both the lady and my father, that red car was not damaged, just dented. All of our family's cars are already none too pretty, so as long as it doesn't affect the workings of the vehicle, we do not care if another dent or scratch appears on the body.
I strive to be a good driver, to keep my hands on the wheel and my eyes on the road.