Hundreds of young people, including Londoners, joined the eleventh edition of the annual No Pants Annual Subway Ride worldwide on Sunday.

The event, which is all about subway rail passengers losing their trousers, was "celebrated" in 50 cities worldwide. To maintain a normal air, the participants take time to chat with fellow passengers, crack jokes, listen to music, read newspapers and keep a straight face as if they are perfectly dressed. Interestingly, other normally dressed passengers, who had no idea what was happening, were left bemused by the thrill-seekers.

The tradition was started in 2002 by Improv Everywhere, a New York-based group, more or less as a prank. But over the years, it has become a popular affair and a global event.

Participants in a No Trousers Day flashmob ride the London Underground transit system with other tube passengers in London.Reuters
Participants in a No Trousers Day flashmob ride the London Underground transit system with other tube passengers in London.Reuters
Participants in a No Trousers Day flashmob ride the London Underground transit system in London.Reuters
Participants in a No Trousers Day flashmob ride the London Underground transit system with other tube passengers in London.Reuters
Participants in a No Trousers Day flashmob ride the London Underground transit system with other tube passengers in London.Reuters
Participants in a No Trousers Day flashmob ride the London Underground transit system in London.Reuters