O'Reilly, the famous Irishman, is driving home after downing a few too many at the pub.  He turns a corner and, much to his horror, sees a tree in the middle of the road.

He swerves to avoid it.  Almost too late, he realizes there is yet another tree directly in his path.  He swerves again and is terrified to discover that his drive home has turned into a slalom course of trees! 

He veers from side to side to avoid all the trees.

Minutes later he hears the sound of a police siren.  He brings his car to a stop.  The officer approaches O'Reilly's car and asks what on earth he was doing.   Shaking, O'Reilly tells the story of trees everywhere in the road.

"Oh for the love of me Saint Joseph!  O'Reilly, that's yer air freshener!"