In photos: Stripping off for a laugh, subway riders worldwide go pantless

On a random day every January, unsuspecting metro users around the globe are witness to a unique phenomenon - hordes of subway travellers...minus their pants. The event, initially started as a prank in New York by the comedy collective Improv Everywhere back in 2002, has now turned into a staple of the global calendar.

The Improv Everywhere website lays down the rules: "Random passengers board a subway car at separate stops in the middle of winter without pants. The participants behave as if they do not know each other, and they all wear winter coats, hats, scarves, and gloves. The only unusual thing is their lack of pants."

And they have their fair share of takers. The last few editions have seen pantless folk the world over riding the subway much to the bemusement of clueless fellow passengers. The challenge is two fold - braving chilly January weather as well as the judgemental stares of those around you, but that hasn't stopped the event from getting more popular with each passing year. This year, participants from dozens of cities including London, Berlin, Philadelphia, Prague and many more took place. These are the best photos from the 2017 edition.