One night, a police officer was staking out a particularly rowdy bar for
possible violations of the driving-under-the-influence laws.  At closing
time, he saw a fellow stumble out of the bar, trip on the curb, and try
his keys on five different cars before he found his.  Then, sat in the
front seat fumbling around with his keys for several minutes.  Everyone
else left the bar and drove off.  Finally, he started his engine and
began to pull away.  The police officer was waiting for him.  He stopped
the driver, read him his rights and administered the Breathalyzer test.
The results showed a reading of 0.0.  The puzzled officer demanded to
know how that could be.  The driver replied, "Tonight, I'm the
designated decoy."