Train Robbery

One day these two guys on a train going to Preswick.  One of the guys needs a dump but there are no toilets on the train so his friend says "Hang your arse out the window and do one."  So his friend pulls down his pants and sticks his arse out the window and just as they're pulling up to the station two robbers on the platform see him. One says "You slap his cheek and I'll steal his cigar".