here's a couple
Yo mama so stupid she hears it's chilly outside so she gets a bowl
Yo mama so stupid you have to dig for her IQ!
Yo mama so stupid she got locked in a grocery store and starved!
Yo mama so stupid it took her 2 hours to watch 60 Minutes!
Yo mama so stupid that she tried to put M&M's in alphabetical order!
Yo mama so stupid she could trip over a cordless phone!
and some more
Yo mama so fat when she has wants someone to shake her hand, she has to give directions!
Yo mama so fat she goes to a resturant, looks at the menu and says "okay!"
Yo mama so fat when she wears a yellow raincoat, people said "Taxi!"
Yo mama so fat she had to go to Sea World to get baptized
Yo mama so fat she got to iron her pants on the driveway
Yo mama so fat she put on her lipstick with a paint-roller