A man rushes into a bar and orders a double martini. He downs it in a single swallow, puts a five-dollar bill on the bar, then turns and rushes out.
The bartender picks up the five-dollar bill, folds it carefully, and tucks it in his vest pocket.
Just at that moment he looks up ... to see his boss standing in the office doorway, staring at him.
"Hi, boss," he says quickly. "Did you see that guy just now? Came in here, bought a double martini, gave me a five dollar tip, and rushed out without paying."