To complicate the issue, let's consider the case that the "other" isn't a person, but a security camera. In the past, there was the presumption that you could maybe get away with a little hanky-panky in public, as long as you were discrete and didn't get caught. We're not talking about behaviors that are illegal in and of themselves - for example, dealing drugs, or engaging in violence. We're talking about a crime that only becomes a crime because somebody who isn't involved happens across it, and doesn't like it.
But does that extend to security footage? If there's a man on the other end of that screen watching, could you be unexpectedly exposing yourself to someone even if you're all alone? (And what if that street cam happens to be peering into your window, or back yard?). Even if there's nobody watching while it happens, law enforcement could conceivably review the footage at some later point in time, and attempt to charge you with exposing yourself to a lamppost.*
Is this as ridiculous as it sounds, or is it something we should legitimately be afraid of? It goes against my belief that if you make a reasonable effort not to disturb anyone (which is quite different from going around intentionally flashing people, as the stereotype goes), it should be considered "no harm, no foul". Certainly, on the list of crimes, with things like mass shootings and terrorism at the top, a naked stroll ought to be considered fairly innocuous. But in this day and age of sexual harassment allegations flying around, not to mention the draconian penalties of the sex offender registry, one can't be too careful.
I've had a relatively lax perspective on privacy for a long time now - obviously, I'm an exhibitionist, and I don't mind so much if people watch. But I'm still afraid that someone will try to reduce my freedom because they simply don't like the way I live. An ever increasing loss of privacy is probably inevitable at this point (if it's not already too late), and there are some advantages such as reducing crime, but for an open world to work (and be anything other than a soul-crushing dystopia), the public and the state both must be perfectly just and tolerant of human diversity. And we're simply not there, yet.
*To get even thornier, if the miscreant happens to be a minor, who gets charged with the production of child pornography? If I were still seventeen years old, I'd totally go around masturbating in front of security cameras just to screw with people. When I was a teenager, I did actually like to sneak out sometimes under the cover of night, to feel the open air on my skin. If I were growing up today, it's entirely possible that I'd be caught - not by a person, but a camera.
And with the proliferation of nanny cams, I wouldn't be safe even in the privacy of my own home anymore, when the parents are out! What worries me is the chilling effect this knowledge might have on this kind of behavior. Sure, we want to discourage criminals, but surreptitious public indecency (not trying to be seen, but trying to avoid getting caught) is fun, totally harmless behavior that I'd like there to be more of in the world, not less. :-(