David Letterman always looks and acts a little nervous when he talks with younger celebrities. He just seems a little out of the loop on who they are and what they do. But in a recent interview with Selena Gomez he finds they have something in common. They have both made Justin Bieber cry. Now, I can't find exactly what Dave is referring to. The only thing I can find is an interview last year where Dave, kind of, lectures Biebs on his tattoos. I've posted both clips below.