Whitney Cummings greeting fans outside Letterman

Fun Fact! Cummings presented Punk'd on MTV in 2004.

Ben Stiller greeting fans outside Letterman studios

Fun Fact! In 1998, Stiller put aside his directing ambitions to star in There's Something About Mary, alongside Cameron Diaz, which accelerated Stiller's acting career.

Just finished taping The @Late_Show with David Letterman (tune in tonight) and met this guy, @JTimberlake backstage...

Fun Fact! Timberlake is a fan of English Football Club Manchester United