Yesterday afternoon, with the temperature in the low 30s, hundreds of people entered the NYC subway system and promptly removed their pants. The occasion was The No Pants Subway Ride, a prank started by Charlie Todd and his Improv Everywhere crew back in January of 2001, and one that shows no sign of losing popularity.

The pantless embarked upon their half-naked journeys on Sunday from six meeting points: in Astoria, Bushwick, Park Slope, the Upper West Side, the Financial District, and the East Village. Although Todd encourages everyone to wear ordinary-looking underwear, and to not add to the joke by wearing costumes, the day has evolved into something of an exhibitionist free-for-all, especially once the various groups arrive in Union Square, where a celebratory scene features dancing and live music.

That's not to say that subway riders aren't often surprised by the shenanigans. Although most pointedly ignore the pranksters in true NYC style, there was also plenty of giggling, eye-rolling, and... creepy ogling.