I was once with a group of professionals and we had all ordered food from various places.

My food came late. Very late. Something had happened to the delivery driver and they had had to find another driver.

Somebody in this group of "professionals" said loudly "I hope you didn't tip."

They wanted me to stiff the person who had come in, possibly on their night off, to solve the problem.

I smiled, said nothing...and increased my tip.