A man stumbles out of a bar one night obviously drunk. He makes his way down the street knocking into everything in his path. A police officer watches him from a cruiser across the street. The man comes up to a parked car, fumbles around in his pockets, gets his keys, and proceeds to drive away. The police officer, unbelieving what he saw, pulls the man over a few blocks down the road. The man gives a breathalizer for the officer and to the officer's amazement - the guy was stone cold sober.
"I can't belive it! I watched you walk to this car, drive erratic all the way down the road, and my machine says you have no alcohol in your system! How can that be???"