Earlier quoted context omitted.
So I'm making an assumption here but... how many orders of magnitude separate your pay and that of the people making your food? Also: how much spit do you estimate you've consumed when eating at places where you're a regular who is known to never tip?
So you see the tip as a sort of bribe to stop those filthy poors contaminating your food?
https://www.gsb.stanford.edu/faculty-research/publications/h...