不著褲乘地鐵日! 2012年1月8日 NYC

The No Pants Subway Ride, an annual event organized by New York City prank collective Improv Everywhere is often erroneously referred to as "No Pants Day." In this event, members of the group enter a subway car at consecutive stops without pants in the middle of winter. Participants pretend that they do not know each other and if asked, claim that they simply "forgot" their pants. The first No Pants Subway Ride took place in 2002 with seven riders and has grown since then. The event has grown considerably over the years. In 2012 nearly 4,000 people participated in New York and tens of thousands more participated in 59 other cities around the world. The fact that the No Pants Subway Ride has become a global event with multiple cities participating on the same day has led to its confusion with No Pants Day. The No Pants Subway Ride is celebrated in early January, with Improv Everywhere usually announcing the exact date a month ahead of time.
參考: Wikipedia