Transit takers lose trousers for 2016 annual No Pants BART Ride

Ashleigh Plasterer reads a book during No Pants! Subway Ride 2016 in San Francisco, Calif., on Sunday, January 10, 2016. Ashleigh Plasterer reads a book during No Pants! Subway Ride 2016 in San Francisco, Calif., on Sunday, January 10, 2016. Photo: Scott Strazzante, The Chronicle Buy photo Photo: Scott Strazzante, The Chronicle Image 1 of / 110 Caption Close Transit takers lose trousers for 2016 annual No Pants BART Ride 1 / 110 Back to Gallery

It might have been a cold 50 degrees in the Bay Area on Sunday afternoon, but that didn't stop groups of bold, bare BART riders from stepping onto the train without their pants.

The No Pants BART ride, a tradition begun by New York's Improv Everywhere years ago, annually inspires denizens of cities across the world to ride public transit half-dressed, just because.

"You do not know any of the other pantless riders," the event page wrote of how participants should behave if someone why they forgot a crucial part of their outfit. "If questioned, tell folks that you 'forgot to wear pants' and yes, you are 'a little cold.' Insist that it is a coincidence that others also forgot their pants."

See the above slideshow to see some of this year's riders from all over the world.