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.

No Pants Subway Ride
A woman has a message for her fellow commuters in New YorkStephanie Keith/Reuters
No Pants Subway Ride
A man takes his trousers off on a New York subway platformStephanie Keith/Reuters
No Pants Subway Ride
A man checks out a woman travelling on a New York subway train in her underwearStephanie Keith/Reuters
No Pants Subway Ride
Two women travel on a New York subway train in their underwearStephanie Keith/Reuters
No Pants Subway Ride
A man travels on a New York subway train in his underwearStephanie Keith/Reuters
No Pants Subway Ride
People dance in their undies at Union Square subway station in New YorkStephanie Keith/Reuters
No Pants Subway Ride
People in their underwear take part in the annual No Pants Subway Ride in New YorkStephanie Keith/Reuters
No Pants Subway Ride
A New York City police officer stands guard during the annual No Pants Subway RideStephanie Keith/Reuters
No Pants Subway Ride
No Pants Subway Ride participants dance on a New York City subway platformTimothy A Clary/AFP
No Pants Subway Ride
A baby snoozes in a pram on a subway platform in New YorkTimothy A Clary/AFP
No Pants Subway Ride
Participants in the No Pants Subway Ride stand on a New York City subway platformTimothy A Clary/AFP
No Pants Subway Ride
A woman pole dances on a train in Washington DCAndrew Caballero/AFP
No Pants Subway Ride
A woman in her underwear has her photo taken in a photobooth at a London Underground stationLeon Neal/AFP
No Pants Subway Ride
People queue for information at Paddington train station in LondonLeon Neal/AFP
No Pants Subway Ride
Participants in the annual International No Pants Subway Ride arrive at Paddington train station in LondonLeon Neal/AFP
No Pants Subway Ride
Two men participating in the No Pants Subway Ride travel on a London Underground trainLeon Neal/AFP
No Pants Subway Ride
People take part in the London version of the No Pants Subway RideLeon Neal/AFP
No Pants Subway Ride
People travel on the London Underground in their underwearLeon Neal/AFP
No Pants Subway Ride
Participants in the annual No Trousers On The Tube Day travel on the London UndergroundPaul Hackett/Reuters
No Pants Subway Ride
A woman in her underwear stands on a Jubilee Line escalator in LondonPaul Hackett/Reuters
No Pants Subway Ride
People take part in the No Pants Subway Ride in BerlinHannibal Hanschke/Reuters
No Pants Subway Ride
A couple pose for pictures during the No Pants Subway Ride in BerlinHannibal Hanschke/Reuters
No Pants Subway Ride
A mother and her son take part in the No Pants Subway Ride in BerlinHannibal Hanschke/Reuters
No Pants Subway Ride
People in their underwear take part in the No Pants Subway Ride in BerlinHannibal Hanschke/Reuters
No Pants Subway Ride
Two men in their underwear wait for a train in Hamburg, northern GermanyBodo Marks/AFP
No Pants Subway Ride
Passengers pose in their underwear as they wait for a train in Prague's subwayMichal Cizek/AFP
No Pants Subway Ride
People stand on an escalator during the No Pants Subway Ride in Prague, Czech RepublicDavid W Cerny/Reuters
No Pants Subway Ride
People stand on a train platform during the No Pants Subway Ride in Vienna, AustriaHeinz-Peter Bader/Reuters
No Pants Subway Ride
People in their underwear sit on a train in ViennaHeinz-Peter Bader/Reuters
No Pants Subway Ride
An Israeli man in his underwear waits for a train in JerusalemRonen Zvulun/Reuters
No Pants Subway Ride
Israelis travel in their underwear on the light rail in JerusalemRonen Zvulun/Reuters
No Pants Subway Ride
A man stares at commuters travelling on a Jerusalem light rail train in their underwearRonen Zvulun/Reuters