Your Mom (born roughly twelve years before you and eleven before her mom) is a well known parent and parental figure. She's celebrated for her dedication to keeping you out of R-rated movies, calling just to "check up on you", and swallowing more semen than the Bermuda triangle, Moby Dick and the cast of High School Musical put together. Despite a certain "lack of credibility" most likely caused by said sluttery, your mom is always there to do your laundry, include love as an ingredient in her recipes, teach your sisters the finer points of pole dancing, or crush you with her massive gravitational pull.
"yo mama's so dumb, she threw a rock at the ground and missed"
"yo mama's so fat, that when she stands on the weighing scale it goes up for a half hour and then says to be continued"
"yo mama's so ugly, she walked into a haunted house, and came out with an application"
"yo mama's so old, she owes jesus 3 bucks"
"yo mama's so fat, that when she was in school, she sat next to everyone"
"yo mama's so dumb, she tried to drown a fish"
"yo mama's so old, I told her to act her age and she turned to dust"
"yo mama's so clumsy, she got tangled in a cordless phone"
"yo mama's so stupid, she stole free bread"
"yo mama's so dumb, she needs a recipe to make ice cubes"
"yo mama's so stupid, she sold her car for gas money"
"yo mama's so fat, she uses a king sizes matress as a tampon"