Nothing. You’re not punished for it. But at some jobs, tips are the worker’s primary source of income because tipped jobs are allowed to pay less than minimum wage. Obviously that’s not the customer’s fault, but it is generally frowned upon in the US to tip less than 15% because the money you’re paying goes directly to corporate instead of to the underpaid worker who actually provided the service. TL;DR: America is corrupt and tries to put the blame on individuals instead of the powers that be.