Your Mama So Fat

Okay, you listen up, you smooth-brained simpleton. You posted this, so you're clearly not the sharpest tool in the shed. The joke is about someone's mother being so large, so big, so absolutely massive that a water bed for her is the size of an entire ocean. That's, like, an exaggeration. It's meant to be funny because it's not realistic at all. It is a roast and uses exaggeration.