I used to work part-time at a slightly upmarket supermarket (we don't have Waitrose in the North West, just Waitrose adverts) and as many of our customers had an overblown sense of entitlement, myself and colleagues were often on the receiving end of a barked "I pay your wages". Here's what I never had the guts to reply:
Yes, yes you do. You are the provider of a miniscule portion of the total revenue that this company receives from its millions of customers. You would therefore appear to be in a position of authority over me, as I rely on another miniscule portion of that revenue for my livelihood. However, this subservient position is one I share with a few thousand other employees, including admin staff, supervisors and management, as well as all of our suppliers and the advertising agencies and other outside contractors this company employs. Let us also, in the hierarchy, not forget our many shareholders. At the same time, you share your position of authority with every other person and company who buys from us which, considering we shop here too, encompasses most of those same people whose wages you claim to pay.
Now, in case you've not considered this economic system in its entirity - this system which you are citing as reason to be rude to me - have a think about where else this vast workforce (and management, and shareholders) spends its money. Please don't forget to take into account the money they pay in taxes, national insurance payments, interest on loans, contributions to pension funds. Can be sure that you are in no way - past, present, or future - a recipient of any of that revenue? Because the economy is not a hierarchy of payers and paid. It is a bafflingly complex web in which there is no straight up and down, no absolute authority or servitude, and in which collectively everyone at some point pays everyone else.
But do not despair, dear customer, for there is another system in place by which we can determine how to treat another human being, despite such a bewildering set of interdependencies. It's known as common fucking courtesy, and if you want me to do as you ask and carry these two packets of organic fat-free rice cakes out to your car for you, you're going to have to show me a little thereof.