The second Saturday in July is a special day for the city of Laguna Niguel in Southern California. Each year on that day, up to 10,000 visitors converge upon the city to take part in the annual, "Mooning Amtrak". The premise is rather simple, visitors line up along the side of the track, drop their drawers, and moon the passing trains.
The "Mooning Amtrak" day is now in it's 31st year, with no visible signs of slowing down. It is widely believed that the tradition came into existence when the patron of a nearby bar, The Mugs Away Saloon, ran to the tracks and mooned a passing Amtrak train on a dare from the bar owner who was offering a free drink to the first person to do it.
For its part, the city of Laguna Niguel, tired of being the butt of jokes, is doing it's best to try and kill the tradition by encouraging folks to stay away, and also passing ordinances that will prevent street vendors from selling to the visitors. It seems to be having no effect though, as the "Mooning Amtrak" website already has plans made for next years event.
I guess they wanna, "just say yes to crack".