Paris Hilton and David LettermanParis Hilton was on 'Late Show' to hawk her new iPhone app, but David Letterman had a better idea. After she showed him the feature that allows you to superimpose a picture of Paris Hilton onto a picture you take of yourself, he decided it would be more fun to drive her boyfriend, Cy Waits, crazy.

"I wonder what the boyfriend thinks of this shot," Letterman said of the first picture Hilton took. It had her leaning provocatively toward him while he was sporting a huge grin.

To make it even better, the producers cut to a shot of Waits off camera, and he did look uncomfortable about the whole thing. That just egged Letterman on. Watch the video after the jump.