I'm with Ruby and not even just "what if a kid sees you", but just - what if anyone sees you? I want to ride the bus, go to the library, sit in class (all places I've seen dudes looking at porn) without seeing it. I think it's gross to expose people to sexual content they don't want to see, in places they wouldn't reasonably expect to see it.
Last month there was a big scandal in Calgary because two guys and a girl were having a threesome in public, and someone recorded it on their phone and posted it online. It was super popular but the fascinating part to me was that a lot of people were saying "don't slut shame!" when people said "that's not cool". (To be fair, some of that was in response to the predictable outcome of people saying "lol she's a whore, get it bros" - but the majority of the responses were "that's gross and inappropriate".) A lot of people were also saying it was wrong of the person to film it. It was a pretty interesting reaction to me.
Can't remember where I read this (I think Tumblr? Sorry if it was here), but basically a lady came into a store upset and wanting to call the cops because there was a man chained to a bike rack, dressed in women's clothes, and she was understandably worried. So the store clerk checked on him. And it was a kink thing - his dom was shopping inside. Again I feel like that's forcing your sex life on others and clearly stressing them out on your behalf, I think that's rude and shitty.
But yeah, really not into porn/seeing people touch themselves/fucking in public. Keep it in places where people go into it knowingly - fuck at sex clubs, get naked at a nude beach (but don't touch yourself there!!!! Just an example of places you can do what you normally can't, haha).