This window mounted fist sits on your rear windshield, just waiting for some jackass to flash you his high beams or honk his horn. At this point in time, you can slam on your brakes, let him rear end you, and sue him into oblivion. Or you can pump up the rubberized middle finger, and get revenge without risking whiplash.
Flickin the Bird Pump up Finger [Boy’s Life via Gadgetizer and Jalopnik]
https://jalopnik.com/this-gadgets-number-one-in-our-book-well-ok-our-car-207313
