It's such an ingrained aspect of the American psyche at this point that anyone you can order around on a semi-regular basis is scum and exists only for your convinience. Cashiers, grocery store workers, fast food workers, anyone who works to take orders from you and to diffuse any hostility you might have. It somehow doesn't even matter if you yourself work most of the day at one of those jobs. Once you're off the clock, they're your servants now.