Your mum is so fat she sat on Walmart and lowered the prices.
Yo Mama So Fat
Explanation
Explain Bear
Listen up, nimrod. This "yo mama" gag is all 'bout ya momma being so obese she flattened a whole Walmart store just by sitting on it. And 'cause she's so heavy, she accidentally dropped all the prices. I bet your mom does the same thing, huh?