More than one thousand subway riders took advantage of the warm weather on Sunday to ditch their pants and startle other straphangers.

“It’s the perfect weather to take off your pants and show off your assets,” said Isabel Fernandez, a 31-year-old filmmaker from Prospect Heights.

The weather was rainy, but in the fifties and warm for January as riders nixed their pants for the 15th year in a row. The “No Pants Subway Ride” started as a small prank in New York by seven members of the group Improv Everywhere, but it has since inspired straphangers in cities all over the world like Berlin and Vienna to commute in their undies.

Katarzyna Pietrzak, a 39-year-old Rego Park attorney, tried to read but kept gawking at the bare-legged riders surrounding her on an uptown No. 5 train.

“Why are you guys not wearing any pants?” Pietrzak asked one pantsless rider, Michael Fadera, a 24-year-old paralegal from Fresh Meadows.

“I have no idea why they’re not,” Fadera said, while a group of girls in bikini underwear casually looked at their cellphones. “I just kind of lost mine on the way here. I really have no idea why they don’t have their pants on.”

Jessica Sirls, a 30-year-old actress and culinary student from SoHo, didn’t participate but said her trip felt much more intimate. “It takes a lot of guesswork out of dating, especially with what some of what these guys are wearing,” she said.

Charlie Todd, the founder of Improv Everywhere, called the day a celebration of silliness.

“I think anybody who’s offended by this event should make sure they don’t take the train to Coney Island in the summer,” he said.