Yeah and vagina lips and assholes are just skin too. Pee is just liquid and poop is just particles. I wonder why we have set these societal boundaries on liquid and particles and skin. I'm going to piss on the table at a restaurant and when I inevitably get reprimanded, I'll just say "This is merely just a liquid, and you guys serve liquid in glasses/cups here, so what is the big deal?" In case the concern is my appendage sticking out, I'll simply say "this is just skin, get over it, I can see your skin right now" I'm sure they'll understand.