Video Evidence: Lauren Conrad, 2008
What started off as standard late-night banter turns south for Lauren Conrad once Dave determined that the star of The Hills didn't have much to offer as a guest. When she started complaining about people she has problems with on her reality show, Letterman asked if, perhaps, she was the problem, and it was off to the races from there.
The best part? The sheer disdain in Letterman's voice when Conrad tells him that she's contracted to write three books.