First, there was the 2009 World Naked Bike Ride:
Chicago's past events included many hundreds of cyclist and numerous inline skaters, and covered over a dozen miles of high visibility city areas. In 2008 the 5th annual event drew a staggering 1700 riders! Blessed by decent summer weather in a great cycling city, the event has grown into a fantastic rolling celebration, with similarities to other major alternative parades world-wide. Participants often describe it as a transcendent group experience, personally transforming, and beyond superlative.Yeesh!
Update: Now even more up-to-date photos.
Then there was this little incident.
How'd you like to explain those road rash scars?