When I was a teenager, I worked as a janitor at McDonalds as my after-school job, and I cleaned the bathrooms. I walked the lobby all the time and could see who was going in and out, and I can assure you (at least back then) there is no correlation between socio-economic class and bathroom etiquette, or mental illness and bathroom etiquette. We had a feces-smearer who was a middle aged lady visiting the restaurant with her normal-looking middle class family. One other fun fact: The men's room was pretty uniformly (but medium) disgusting, but the women's room was where the variance was. I saw foulness in the women's restroom that haunts me to this day.