as a father of two teenagers who eat like four, in mexico city you leave ten percent, maybe fifteen if the waiter was kind to the kids, and it is a thank you not a rent payment, but last month i was in houston for work and the machine at a taco counter turned around and asked me 15 20 or 25 before i had my food, in front of the young man who made it, and i pressed 20 because he was looking at me, and then i stood there thinking i just paid a tax to not feel like a bad person, and my company reimbursed it so it was not even my money, but i still felt it, and i think that feeling is the whole business model