The toilets/restrooms at restaurants (or at least many fastfood restaurants?) are often shared and used by both employees and customers. It grossed me out a bit a bit at first, especially as they are, in my experience, quite often pretty filthy. So all the nastiness customers drag in could potentially be picked up by employees.

I've been to BKs and Wendys' where I left the establishment as soon as I entered, just because the whole place looked and smelled like somewhere you shouldn't eat. I suppose these were more often than not in pretty rural areas..

While on the toilet topic, I've found public restrooms at e.g. gas stations and shopping malls to often be, uh, less than inviting. I think I've seen more overflowing toilets on a 4 week vacation in the US than I've seen in 40 years over here, in northwest Europe.

To be fair, I've driven east/west at least 10 times over the years, so I've been to a lot of public restrooms and the bad experiences tend to stay with you for longer than the good ones.