Muni, BART riders lose their pants

Transit riders around the world, including those on BART and Muni, took part in a "no pants subway ride" Sunday.

The event first began in New York in 2002 and has now spread to 44 transit systems in 16 countries.

The flash mob is organized by a group of pranksters called Improv Everywhere.

There is no ulterior motive; participants simply get on a train and ride without pants.