Not very PC but here you go!
As he stood in front of the Pearly Gates behind St Peter, he saw a huge wall of infinity covered with clocks.
He asked, 'What are all those clocks?'
St. Peter answered, 'Those are Lie-Clocks. Everyone on earth has a Lie-Clock.
Every time someone lies the hands on their clock move.'
'Oh', said the man. 'Whose clock is that?'
'That's Mother Teresa's', replied St. Peter. 'The hands have never moved, indicating that she never told a lie.'
'Incredible', said the man. 'And whose clock is that one?'
St. Peter responded, 'That's Abraham Lincoln's clock. The hands have moved twice, telling us that Abraham told only two lies in his entire life.'
'Where's Gordon Brown's clock?' asked the man.
'Ah! Brown's clock is in Jesus's office. He's using it as a ceiling fan.'