One night, a police officer was staking out a particularly rowdy bar for potential violators of the driving-under-the-influence law. At closing time, the officer notices a patron stumble out of the bar, trip on the curb and try his keys on six different cars before finally finding his own. The fellow then opens his car door and proceeds to sit in the front seat.
By now, everyone else has left the bar and driven off.
After some trouble, the fellow starts the engine and begins to pull away. The police officer stops the driver in his tracks, reads him his rights and administers a breathalyzer test. Amazingly, though, the results show a reading of 0.00. The puzzled officer demands to know how this could be. "I don't get it. You stumbled out of the bar, triped on the curb and tried your keys on six different cars before finally found your own. How can it be that you blow 0.00?"
Replies the driver, "Fooled you, sir... I'm just the designated decoy."