Your mamma's so poor, I stepped on a cigarette butt and she said "Who turned out the heat?"
Your mamma's so stupid, she gets her facts from World Weekly News.
Your mamma's so fat, her clothes size comes in light years.
Your mamma's so ugly, she looked into a mirror to commit suiside.
Your mamma's so old, she gave birth to your grandmother.
Your mamma's so fat, when she slept an air bed, it popped.
Your mamma's so fat, she's only allowed on the ground floor of buildings.
Your mamma's so stupid she makes YOU look inteligent.
Edit: Your Pappa's so stupid he married your mamma.