In the radical little village that I live in we once had a good laugh.
We were in the middle of a very large police opperation that went on for six months. Somewhere in the middle of this a parking warden came out from the local city council. He came out of the police station, walked down one side of the street chalking the cars then proceded up the other side back towards the police station, eventually chalking every car in the village.
As soon as he entered the station one of our more radical young females got a wet rag and rubbed every mark off every tyre.
An hour later he came out of the station, we all watched him walk back down the street, checking the cars. When he reached the pub, where we were, he seemed to realise he had been had and just turned on his heels and went back up the same side of the street to the police station, got in his car, and left.