Thousands Go Bare in Worldwide No Pants Subway Ride

1. New York City

   Photo courtesy of Instagram, slepka

   

2. Mexico

   Photo via Ronaldo Schemidt/AFP/Getty Images

   

3. Hong Kong

   Photo courtesy of Instagram, wesmark.

   

4. Boston

   Photo courtesy of Twitter, e_baldi

   

5. NYC

   Photo courtesy of Instagram, bigxay

   

6. Washington, D.C.

   Photo courtesy of Instagram, armandogv

   

7. NYC

   Photo courtesy of Instagram, josephpadiernos.

   

8. Mexico

   Photo courtesy of Instagram, joseserrano14

   

9. NYC

   Photo courtesy of Instagram, pon_say

   

10. Bulgaria

    Photo via Nikolay Doychinov/AFP/Getty Images

    

11. Atlanta

    Photo courtesy Instagram, f_marc

    

12. NYC

    Photo via Timothy A. Clary/AFP/Getty Images

    

13. Philadelphia

    Photo courtesy Instagram, agpcollective.

    

Commuters in subway stations around the globe were turned into peeping Toms on Sunday, as many unwittingly faced their fellow travelers' underclothes.

Straphangers got an eyeful during the 12th annual No Pants Subway Ride, a prank started in 2002 by Improv Everywhere. The New York City-based group calls themselves a "prank collective that causes scenes of chaos and joy in public places." And what could possibly bring more joy than strangers in their underwear?

Thousands participated in more than 25 countries, including China, Australia and Mexico. In Seattle, pranksters braved 37-degree weather sans pants.

There are only two requirements: Take 'em off and keep a straight face. No thongs or other offensive underwear are allowed, but everything else is fair game.

Participants are organized into groups and assigned a specific train car, but can't speak to one another. The first No Pants Subway Ride had just seven men and a pants peddler who later came through the car with a duffle bag. This year, NYC had more than 4,000 bare-bottomed pranksters.

Check out this year's video and take a peek at our gallery, above, of pants-less people around the world.

Thumbnail image via Timothy A. Clary/AFP/Getty Images