Already seen a few of my favorites listed, but the best one I saw matched the car perfectly. Me and the kids pull up to the red light... we stop behind a car that the rear bumper and trunk is nearly even with the back window, duct tape holing the lights in place, brake light tape over the brake lights, and bungee cords holding the trunk lid down....
Right in the middle of all this was a sticker that read "HONK IF A PART FALLS OFF"... We all busted out laughing, and still joke about it today. That was 3-4 years ago.