A passenger not wearing pants sits in a subway train during the “No Pants Subway Ride” in Prague, Czech Republic, January 10, 2016. The event is an annual flash mob and occurs in different cities around the world in January, according to its organisers. (Photo by David W. Cerny/Reuters)

Subway passengers walk past bronze sculptures representing the Soviet people at the Ploshchad Revolyutsii metro station in Moscow, on November 14, 2012. The station was opened in 1938. (Photo by Kirill Kudryavtsev/AFP Photo)

Passengers wear no trousers as they ride the London Underground in London, Britain, 07 January 2018. The No Pants Subway Ride is an global annual event where people take the public transport while they are not wearing trousers to surprise other passengers. This event takes place on the first Sunday of every year in the world's major cities. (Photo by Tolga Akmen/EPA/EFE/Rex Features/Shutterstock)

A woman travels on a train stopping at a subway station visited by foreign reporters in central Pyongyang, North Korea on April 14, 2017. (Photo by Damir Sagolj/Reuters)

A dressed up participant without trousers takes part in the 2017 No Pants Subway Ride in New York, the United States, on January 8, 2017. The event, which first took place in New York in 2002, has become a yearly event attended by people in more than 60 cities across the globe. (Photo by Zou Zheng/Xinhua/Sipa USA)

A passenger takes off his pants as others not wearing pants dance while waiting for a subway train during the “No Pants Subway Ride” in Mexico City, Mexico, February 21, 2016. The event is an annual flash mob and occurs in different cities around the world, according to its organisers. (Photo by Carlos Jasso/Reuters)

Participants gather in the Union Square subway station during the annual No Pants Subway Ride on January 8, 2012 in New York City. The annual event is staged by the group Improv Everywhere which encourages people in dozens of cities worldwide to discard their pants while riding the subway. (Photo by Mario Tama/Getty Images)

Commuters walk up the redesigned subway stairs at the Tanjong Pagar subway station on August 23, 2011 in Singapore. The subway stairs have been repainted in bright colours and slogans encouraging people to take the stairs, by way of promoting fitness in the city. (Photo by Chris McGrath/Getty Images)