Pants were optional on BART Sunday

Normally, if someone on your train isn’t wearing pants on your BART train, it’s a good sign you might want to change cars.

That wouldn’t have helped on Sunday afternoon, as hundreds of pantless-riders organized flash-mob style to treat surprised downtown riders and visitors to a fine view of their bottom halves.

For years, New Yorkers have stripped their pants and joined other surprised straphangers in their subterranean journeys. The stunt has grown into a global phenomena, with riders all over the world now participating in the pants-free Sunday.

Facebook shows 627 people signed up to show some portion of their bare skin in the Bay Area on Sunday. The group organized into two main boardings, emerging from BART in the early afternoon before transferring to Muni on their way to Levi’s Plaza Park.

After getting kicked out of there, the group meandered to North Beach, no doubt entertaining tourists and passers-by the entire way.