Diet Dr Pepper TV Commercial, 'Lil' Sweet: Birthday' Featuring Justin Guarini

American Idol alum Justin Guarini returns as Lil' Sweet in this new Diet Dr Pepper commercial, this time making a special appearance at a birthday party. He slides down the banister (while singing that he's sliding down the banister) right after two guys say they wish they could eat a cupcake without the calories. Lil' Sweet reminds two men that they can skip the cupcake calories and enjoy the sweeeeet zero-calorie Diet Dr Peppers. Now, excuse Lil' Sweet while he defies gravity and goes back up the banister.