It's Always Sunny in Philadelphia: Season 3, Episode 5

3 - 5: The Aluminum Monster vs. Fatty Magoo

Dee gets a rude awakening when she discovers that "Fatty Magoo," an overweight loser from her high-school class, is now a svelte, successful clothing-store owner. So Dee decides to design a dress for her, but Dennis decides that he's the better designer. He also knows that he has the charm to sell it to Fatty (Judy Greer).