Well, this isn't fast food, but an experience from when I was working in a restaurant one summer when I was 17.
I was a hostess, but on one day the restaurant was really busy and short handed with wait staff. One of the waitors asked me to help him by taking a table's food out to them, which I was happy to do. Well, the table was full of businessmen (in their 30s I'd say) out to lunch, and when I asked them if I could get them anything else, one of them says to me, "How 'bout a hot tub and a rub down?" I was totally speechless and embarrassed...and you could see that his coworkers were
that he had just said that to a teenage waitress at their business lunch!