"Road rage is when people actually lose control," says Conrad King, a psychologist with the Royal Automobile Club. "It's kind of like having a temper tantrum. But you are having the tantrum when you are in control of a lethal weapon which is what a car is."
In Scotland, Robbie Crawford says he became a devil in his white sedan.
"I can't believe I let myself get in that situation," says Crawford. Road rage? "That's it. That's exactly what it was."
But while losing his temper, he found inspiration: an invention into which he has now poured his life savings.
It's a message board for motorists that he's selling for $60, now lighting up rear windows in a handful of cars -- with a limited built-in vocabulary designed to appease.
You push the button for "sorry" and you can get away with almost anything, says Crawford. "It's incredible -- it instantly deflates anything that's going on."
A dashboard control means he never has to say he's sorry; he just sends a message, apologetic or grateful.
Now he hopes it will help bring calm to the road, make him a millionaire and, if the need arises, get him out of trouble.