Sunday was the 12th annual No Pants Subway Ride day, staged by the Improv Everywhere group in New York City.
The event began as a small prank with just seven participants and has since grown into a worldwide phenomenon with participants in 26 countries.
Participants are encouraged to forgo wearing pants, but remained fully clothed otherwise, including underwear, shirts, jackets, hats and footwear.
"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," the Improv Everywhere website said.