This is from Will & Guy’s joke site.
One night Rodney was driving home along a road he knew well. When he reached the Stop sign he slowed down but did not actually come to a halt, whereupon a police officer pulled Rodney’s car over.
‘What difference does it make,’ said Rodney, ‘slow down or stop?’
‘I will give you a demonstration,’ said the officer, and he began to beat Rodney with his truncheon. ‘Now, would you like me to slow down – or stop?’