I know this makes me a dinsosaur in this day and age, but I actually do self-censor. For example, when on public transport I try not to have conversations about people's sex lives, the gory details of medical conditions, or contentious religious topics. At work, I don't use certain words that I throw around with abandon on my own time (except when I broke my ankle at work and it all just spilled out in a blue streak).

I have sat next to somebody on a plane who was looking at graphic, violent porn, and while I wouldn't ask him to stop, it was pretty creepy. On my bus to and from work over the years I have been treated to more phone calls than I care to count of people cursing out and threatening their boyfriends or girlfriends, detailing sickening medical facts, recounting sex acts, throwing around racist epithets, etc.

I'm not saying that this necessarily applies to watching a video with occasional "adult" scenes, which I personally would find harmless. But by the same token, I don't quite get why it's necessarily unreasonable to be expected to moderate one's actions when in public places.