The worst attitude should be reserved for the infamous "PWA customers". Of course PWA is a old service station abbr. for the customer who comes into the station and wants to use the restroom, get water (to drink or for his radiator, I’ve never been sure) and air in his tires. I’ve heard this term used in diners around central New York State several times in the semi-distant past.
Of coure in my own business (which has nothing whatsoever to do with food) we have customers whom I’ve nicknamed "PTW" which, of course stands for "professional time waster".
Furthermore, many times I’ve wanted to ask the question of a customer: "What do I look like, a reference librarian?"