> It's extremely common for there to be human shit in the train cars, and lunatics going nuts

Where does that come from? Not from your experience. You've never been on NY subways, clearly.

I've never seen feces - and anyway, how could you tell if it's from a dog? Did you examine it? Take it home and test it? It's one of the stories that maybe is slightly plausible, and which yields such strong disgust that rationality is overwhelmed and it makes a sensation - perfectly constructed misinformation or urban myth. Like waking up in a bathtub with a kidney missing.

'Lunatics' is such a loaded (and hateful) word you'll have to specify what you mean, but the occasional person talking to themself is harmless and completely uninterested in you (thus the conversation with themself) - I have never had any problem with such people on public transit or elsewhere. They are the most vulnerable people and compassion is the appropriate response.

As I wrote above, the stories are nonsense and it's induced fear.