Once when I worked as a barista we were super busy. Two people on the coffee machine at all times but people were ordering 5-10 drinks at once so we were a little more backed up.
Well our District Manager just happened to be there that day helping us out. An older gentleman saw this and decided to try to take advantage. After he gets his coffee, he decides to throw a hissy fit about how he has to wait fifteen minutes and how that is unacceptable and now he wants his drink to be free to compensate.
Our District Manager goes over to the screen, scrolls back to find his order, looks at the time stamp and tells him, "Sir, even with your outburst it has still only been 4.5 minutes. You aren't getting anything for free."
She was pretty much the only boss I ever liked at that place.