Sticking your arm outside the window to give the bird can be too much effort sometimes. Driv-e-mocion is the perfect device for the ultimate lazy aggressive driver. It is a small electronic display that can attach to the back window and allow any kind of message include smilie faces, frownie faces, kind words and even some four-letter words to be displayed. Given, the four letter words may anger the person behind you even more, it is still cool to put them in their place, geekily. $20 for an increased chance of being ran off the road, worth it to me.
are you sure, iross? what about reversing lights and indicators?
I think these would be great with polite messages like "sorry" and "thanks" in, also I'd like it to show a speed limit sign with my speed in it whenever I'm going much slower than the speed limit. This would let the *@@£# approaching in the Audi at 90mph know that he'll have to shed 28MPH pretty sharpish to avoid hitting me up the behind.