The last Sunday of September brings the world's largest S&M/leather event (with 400,000 attendees) to SOMA, replacing the usual car traffic with a sea of skin and black-leather.
In addition to an astounding variety of sexual expression, the fair has a large number of shopping and demonstration booths, (usually) surprisingly good bands (on multiple stages), plenty of dancing and the usual collection of fair food and alcohol. The crowd is more gay/male than anything else, but the anything-else contingent makes a strong showing :)
Organizationally, it is the oldest of the street fairs in San Francisco and still the model of organization and success.
And, if it doesn't go without saying (!?), this is not an event for children - there is both nudity and public sexual activity.
Not your cup of tea? The neighborhoody Castro Street Fair and Hardly Strictly Bluegrass arrive the following weekend :)
Address: SOMA, SF
Website: http://folsomstreetfair.org/
Wikipedia: http://en.wikipedia.org/wiki/Folsom_Street_Fair
