What made Ricky Gervais howl with laughter on David Letterman?

The Derek comedian had a right blast on the American chat show...

Ricky Gervais gave his facial muscles a good old work out on the Late Show with David Letterman this week. The Office and Derek funnyman was sent into fits of giggles by the veteran host’s enquiries into his private life… 


But what was the cause of his prolonged chortling? Well, you’ll just have to watch the video to find out, won’t you?