One night a police officer is staking out a particularly rowdy bar for possible DUI violations.
At closing time, he sees a fellow stumble out of the bar, trip on the curb and try his keys on five different cars before he finds his.
The man then sits in the front seat fumbling around with his keys for several minutes.
Meanwhile, all the other patrons left the bar and drove off.
Finally the fellow starts his engine and begins to pull away. The police officer is waiting for him.
As soon as he pulls onto the street, the officer stops him, reads him his rights and administers the breathalyzer test to determine his blood-alcohol content. The results show a reading of 0.0.
The puzzled officer demands to know how that can be.
The driver grins and replies, “Tonight I’m the designated decoy.”