For the last decade, there's been an annual "prank" done by New York based Improv Everywhere.  This event has also been picked up other major cities in the U.S. and other countries.  Participants respond to a Facebook invitation and ride the subway without wearing their pants. According to AfterElton: 

When Hudson Taylor isn't busy coaching wrestling at Columbia, fighting homophobia, or working with his Athlete Ally foundation, he likes to have fun, like participating in the 10th Annual No Pants Subway Ride (with his wife).