The No Pants Subway Ride is an annual event staged by Improv Everywhere every January in New York City. The mission started as a small prank with seven guys and has grown into an international celebration of silliness, with dozens of cities around the world participating each year. The idea behind No Pants is simple: Random passengers board a subway car at separate stops in the middle of winter without pants. The participants do not behave as if they know each other, and they all wear winter coats, hats, scarves, and gloves. The only unusual thing is their lack of pants.
More information, including videos from previous years, can be found here.