A plumber came knocking at Mark's door. "I've come to fix your blocked toilet" the plumber said. "We haven't got a blocked toilet" Mark replied. "Are you Mr Collis?" the plumber queried. "No" Mark answered. "He moved away six months ago". "There are some real bastards in the world" the plumber swore. "They ring for a plumber saying it's an emergency, then they piss off to another address".