Found on http://twentytwowords.com/one-tiny-japanese-driving-habit-that-could-end-road-rage-in-america-why-dont-we-do-this/
It was early when I posted this, and the coffee hadn't kicked in yet, so I forgot that truckers int eh US do this, and lots of drivers who have caught on to using the double brake tap or flashers to let a trucker know "Thanks" or " Cut in" ... when you see the comments, you'll see that this happens in many countries