I was driving along today on a surface that I wasn't entirely sure of, in my shiny new car. And a buffoon comes up behind me in a BMW and decides to see if they can actually see themselves in my rear view mirror. If I had needed to brake I'm sure we would have had an unpleasant and expensive "two become one" moment. Fool.
In the Good Old Days (tm) we had a Ford Cortina which had a towing bracket on the back made of angle iron. Think the kind of stuff they use to hold up the girders in buildings. In this situation we were without fear. When somebody drove into to the back there would be an enormous crash and a cloud of steam from their shattered radiator. We'd get out and notice a tiny scratch on the ironwork. They'd have to buy a whole new car front. And quite right too.