My friend is often dissatisfied with restaurant service and therefore tips poorly, even in cases when it’s not the waiter’s fault. This reflects poorly on me too, and I don’t want to eat out with him. How do I explain this? —Anonymous, Seattle
WHEN THE BILL arrives, calculate how much your friend is undertipping. Add that amount to your tip and say to the waiter: “My friend and I have different opinions on tipping. I think it’s important, and he doesn’t.” This will potentially shame your friend into behaving differently. Of course, he may never change—and you may anger him. But if you view something that’s technically optional as socially essential, you have to accept responsibility for upholding that belief.
—Adapted from “The Ethicist” in The New York Times Magazine