Recurring on It's Always Sunny in Philadelphia helped land Simpson the role of David Letterman's repugnant, d*ckish Lyle the Intern from 2008 through 2009. "It's something about my face," says Simpson in an interview for Letterman's YouTube channel. "My face just looks like I might be a d*ck. And I'm fine with this. It's kept me working in this industry." Simpson also reveals he's never interacted with Letterman as himself.