There's that old joke about these cops sitting outside the local bar, waiting for drunks to leave... when they see this guy stumbling out and all over the parking lot. He keeps dropping his keys, and tries three or four cars before he finds the right one. The guy finally gets the car started, and commences to weave all over the road on his way out.
The cops give chase... finally pulled the guy over... but the guy totally passed all the tests... even the breathalyzer... One cop says "What's wrong with you-- you're completely sober... "
"Tonight" the guy says "I'm the designated decoy."
Yep, I've heard that one! Not sure it would amuse the cops...