Late one night a cop is sitting in the parking lot of the local tavern
watching for drunk drivers.  A guy come out, tries his keys in a car but
they don't work.  He tries another, they still don't work.  Now people
start leaving the bar.  Eventually there is only one car left.  The guy
tries his key and opens the door.

The cop comes roaring over with his lights on, gives the guy a breathalyzer,
- but the guy blows a zero!

The cop asks, "are you the designated driver?"

The guy responds, "No, I'm the designated decoy."