If you rode a subway in a major city somewhere in the world today, you might have noticed some people were not wearing pants.

They're not perverts, but rather participants in the annual "No Pants Subway Ride Day" (video below).

This unusual holiday started in New York City in 2002 and has spread around the globe to cities such as Sydney, Beijing, Hong Kong, London, Paris and Berlin, reports RT.com.

"No Pants Subway Ride Day" was created by Improv Everywhere, a performance art group, which originally included only seven pants-less men riding the subways in New York City.

These days the pranksters travel in groups. They agree where to meet, walk to the subways with their pants on, remove their trousers, get off and board at various spots and and always act completely normal.

While shocked passengers look on, the pants-less folks read a paper, text on a cell phone or just chat.

According to the Daily Mail, Sydney, Australia groups were instructed how to respond to passengers who ask about their lack of pants on Facebook: “If questioned, you do not know any of the other pant-less riders. Tell folks that you 'forgot to wear pants.' Insist that it is a coincidence that others also forgot their trousers. Be nice, friendly and remain calm."

“It's the first time he will be publicly taking off his pants, although he does it regularly already,” Australian Bess Hepworth told AFP about her 18-month-old son.

In the US, people dropped their pants in subways in Boston, New York, Chicago and San Francisco.

Sources: Daily Mail, AFP, RT.com, Improv Everywhere