I've known many who "kill them with kindness" and still are regularly stiffed. For example, my cousin worked in a nightclub as a waitress. She put up with some pretty heinous treatment and kept her smile in place the whole time. She still was regularly stiffed. Couples were the worst tippers.

I and three of my sisters worked as waitresses at times too. You can give the best service possible, smile through the abuse, and still watch them leave without tipping. In a lot of settings, waitstaff are lucky if the patrons drop their loose change on the table.

When we owned our cafe, the waitress/barista rarely got more than a handful of change dropped in her jar, no matter how large the order. And, we often had large orders for office lunches or meetings.

Also, there are regions of the country where people are just plain beligerent about an expection of tipping. I've lived and traveled in those regions all my life. Specifically, the Southest, the Mid-South, and the Mid-West.