It's just generally not a good idea to be rude to employees in general.
i never am. that doesnt stop a lot of them having shitty attitudes
This is usually the attitude of someone who has never worked in restaurant or retail and thinks they should have their feet kissed walking through the door because the mighty savior paying everyones salary just walked in. A lot probably translates to a tiny percentage of cashiers/employees and waiters/waitresses youve actually encountered.
Im hyper aware of how people behave in those situations due to my background and the vast majority of cashiers, floor employees and waiters/waitresses/counter people are at least courteous if not pleasant. Not sure what your standards demand but not a lot of them are the awful people youre making them out to be.
You say "never worked in retail" as if thats a bad thing... ---