Seeing one person on a BART train not wearing pants isn't anything to write home about--a funny story good for a chuckle around the water cooler the next morning, but not much else.
Seeing several hundred pants-free people on a BART train, on the other hand, is different story entirely.
Getting as many of those reality-questioning double takes as possible is the ultimate goal behind the "No Pants BART Ride" that happened this Sunday.
(SCROLL DOWN FOR PHOTOS)
The brainchild of New York-based reality pranksters Improv Everywhere, the No Pants Subway Ride is an annual event, currently in its eleventh year, where participants take off their pants and ride around on the nation's transit systems acting like nothing out of the ordinary is going on.
Don't worry, everyone is supposed to at least wear underwear. We sure hope they did, because BART seats aren't exactly sanitary.
Exact pantsless ridership estimates are difficult to ascertain; however, over 600 people signed up for the event's Facebook group.
The ride is coordinated worldwide with similar events happening in places as disparate as Salt Lake City and Adelaide, Australia.
Check out this slideshow of pictures from the event, courtesy of Bhautik Joshi:
Check out this video of Improv Everywhere's founder giving a talk about the event at the annual TED conference: