The World Naked Bike Ride kicks off at 11 a.m. in San Francisco, and it will be quite nipply out there.

This is actually SF's 10th annual World Naked Bike Ride, though naked bike rides were happening well before 2010 elsewhere. (Portland's annual version happens in late June, which makes way more sense.)

"We meet northwest of the Ferry Building, between the Farmer's Market and the Starbucks west of the Ferry Building," write the organizers in a Facebook post. "We begin gathering at 11:00 AM in the open area along the pier... We will have time to do body/face paint and reacquaint ourselves."

Also, they note, "While it is a "naked" bike ride, all are welcome. It's ride as bare as you dare. That is, body paint, rubber latex, bikinis, topless, lingerie, bubble pack, whatever costume you are comfortable riding with."

And while you may think it's just frivolous naked fun, this event is actually a protest of "the global dependency of our society and economies at the hands of the oil cartels." Say the organizers, "We want to emphasize the harm this dependency causes to our environment, businesses and social lives."

As NBC Bay Area tells us, the naked bike ride will head past Fisherman's Wharf to the Marina, Lombard Street, North Beach, Civic Center, Haight-Ashbury and the Castro, perhaps not in that order, and riders can join in whenever they like.