A man died and went to Heaven. As he stood in front of the Pearly Gates, he saw a huge wall of clocks behind him. He asked 'What are those clocks?'.
St. Peter replied 'Those are Lie-Clocks. Everyone on Earth has a Lie-Clock. Whenever you lie, the hands on the clock move. This one here is Mother Teresa's. The hands have never moved so she has never lied. That one over there is Abraham Lincoln's. It moved twice, so he only lied twice in his whole life.'
'Well, where's David Cameron's clock?' asked the man.
'It's in my office, I'm using it as a ceiling fan'.