Critical_Mass,_San_Francisco,_April_29,_2005_4.jpg
Credit: Wikipedia

As bike culture grows, so too does bicycling as a form of celebration and protest. Two incarnations of this trend are the World Naked Bike Ride, whose phantasmagoric website describes its aims as using naked bodies to "defend our dignity and expose the unique dangers faced by cyclists"; and Critical Mass, which, on the last Friday of every month, takes over the streets to "draw attention to how unfriendly the city is to bicyclists."

Both groups have recently held events in Vancouver.

Vancouver Naked Bike Ride 2008

Vancouver Critical Mass 2007

Extra: More bare butts in Brighton