Bloke serving a prison term, ends up sharing a cell with the biggest most violent murderer.
During the 1st night, the murderer announces "we're goi'n to have a game of mummies and daddies, who do you want to be, mummy or daddy ?".
Thinking fast and fearing the worst, he replies " i'll be daddy", to which the murderer replies " right mummy wants a blow job !"