You're a little slow on the uptake, Scott (the World Naked Bike Ride was two weeks ago, and you're just now noticing that the people were naked?), but I like the cut of your jib. I don't want to see it—your jib should probably stay reefed—but I like the cut of it.
Public nudity is broadly legal in Oregon—state law says you can do as you like, as long as you don't do it with the intent to cause arousal in others.
To put it another way, nudity is legal in Oregon as long as there's no chance that anyone might be enjoying it. It's the same logic that left your middle-school library choked with 80-year-old Papua New Guinea boobies in National Geographic, but utterly devoid of Juggs magazine.
But that's state law. In hippy-dippy, free-love Portland, just like in that town in Shirley Jackson's "The Lottery," your nards are a crime whether they give anybody a boner or not.
Here, if your junk is out where a person of the opposite sex can see it (obviously, no one could possibly be aroused by a member of the same sex), you're guilty of indecent exposure under city ordinance 14.24.060.
Unless! Under the precedent set in 1985's Portland v. Gatewood (just call me Jack McCoy), wang-dangling can be permissible if it's in the service of a political message. This is the legal gloryhole that the Naked Bike Ride thrusts itself through.
The upshot is that if you're planning to drop trou on Live @ 7, as your attorney, I recommend first writing "Free Edward Snowden" across your butt cheeks.
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