Anthony Gill mulls tipping: "To paraphrase a recent student comment on a class discussion board: I don't think tipping (leaving a gratuity) has anything to do with economics. It is a matter of psychology. People just like different things and try to do those things the best they can."
Is tipping euvoluntary? Recall what Mr. Pink said.
Remember Adam Smith's advice: use sympathy. From the customer's point of view, the restaurant transaction is a singular event in the course of the day. The interaction with the wait staff is judged on its relative merits, gratuity to be determined by a combination of perceived quality of service and a baseline norm. But from the point of view of the server, each table is one of a multitude of interactions.
The best servers I've worked with follow a sort of script, one designed to mimic the appearance of a personal encounter, with small elements of genuine personal touches thrown in. Still, when it comes time to tally up the day's take, numbers matter, specifically those numbers preceded by currency symbols. Customers care about their idiosyncratic dining experience, servers care about their aggregated earnings. And both do their parts embedded in a suite of institutions that generate expectations for behavior. Buscemi delivered the antisocial tirade, not Madsen. This was not an accident of casting.
The curious bit is the relationship of low-cost information to tipping institutions. Stiff-shaming is easier than ever, and we've seen several hoaxes cost people their jobs already, so I'd be curious to see what overall impact this might ultimately have on gratuities. Curious.