Designated Drunk

One night at a local bar frequented by a bunch of deer hunters who were waiting for the opening day of deer season, the local sheriff scoped out the joint for possible drunk drivers.
As he waited, eventually a patron stumbled out of the bar, fumbled for his keys, tried them in three different cars until he finally found his, got inside and rested his head on the steering wheel. The deputy knew he had his drunk driver, so now all he had to do was wait for him to start his engine and pull out of the lot.
A few hours passed by and most of the other deer hunters had left by then, when the patron abruptly lifted his head, cranked the car up and drove out of the lot like a bat out of hell. The deputy followed him and stopped him promptly. He administered the breath-o-lizer test and it read 0.00.

Confused, the deputy asked the driver what the hell was going on. The driver looked at him innocently and said, "Well, tonight I'm the designated decoy."