Thousands of train commuters in 60 cities around the world stripped down to their underwear on public transport for the annual No Pants Subway Ride. The idea is for participants to maintain a nonchalant air, chatting with fellow passengers, listening to music, reading newspapers, while keeping a straight face as if all were perfectly normal.

The No Pants Subway Ride began in 2002 in New York with only seven participants and has grown into a global phenomenon. Organisers call it "an international celebration of silliness". The event is coordinated by Improv Everywhere, a global flash mob. Even families took part, carrying babies wearing just their nappies. A Berlin woman had a cat's face splashed across her cheeks. At London stations, coats and scarves warded off the chill — at least from the waist up. Participants in Jerusalem drew stern stares from Ultra Orthodox men.

IBTimes UK rounds up some of the best No Pants Subway Ride photos from around the world.