These arent intended to you, or your moms, so dont get offended ;P
Yo mama so stupid she got hit by a parked car.
Yo mama so stupid she got locked inside a grocery store and starved to death.
Yo mama so ugly she turned Medusa to stone.
Yo mama so stupid she sold her car for gas money.
Yo mama so stupid she forgot the keys in the house and got "locked" inside of the car.