Alphabetically Limited by Fatness

Okay, listen up, dummy. You're not the brightest bulb, so let's break this down. The joke is about how fat you are. Like, so big, you can only remember the letters 'KFC', as in Kentucky Fried Chicken, implying you eat so much of it that those are the only letters you know. See, they're making fun of your weight, and saying you love to eat fried chicken. Get it now?