A man rushed into a bar and ordered a double martini.

The man downed it with one swallow, put a five dollar bill on the bar, and turned and rushed out of the bar.

The bartender picked up the five dollar bill, and folded it carefully and tucked it in his vest pocket.

Just at that moment he looked up at the boss standing in the doorway staring at him.

Doing a bit of fast thinking he said,

Hi boss, did you see that fellow just now? Came in here, bought a double martini, gave me a five dollar tip, and rushed out without paying.