Hundreds of people in Mexico City shed their pants and skirts to take part in the "No Pants Subway Ride" prank, just for laughs, around the world.
Young and old of all ages participated in the stunt Sunday in the Mexican capital, held once a year in dozens of places, the movement said on its website.
Organized by New York City-based prank collective Improv Everywhere, the annual event was launched in 2002 and has since spread to more than 60 cities.
In places as far apart as Bangkok, Jerusalem, London, Sofia, Stockholm, New York and Washington, participants -- fully clothed on top -- rode the subway while showing off their panties, briefs and boxers, according to organizers.
Many wore sunglasses, while some donned brightly colored underwear and socks.
Improv Everywhere asks participants to abide by two requirements: being willing to strip down and keeping "a straight face about it."
While the first "No Pants Subway Ride" had just seven participants, recent renditions have counted nearly 4,000 in New York and thousands more around the globe, according to Improv Everywhere.
The prank collective's founder Charlie Todd called the event a "celebration of silliness," and said its goal is simply to make others laugh and smile.