So, so generic.
Your momma's so hairy, the only language she speaks is wookie. *wookie noise*
Your momma's so stupid she stole free bread from a sample stool.
Your momma's so stupid climbed over a glass wall to see what's on the other side.
You momma is so fat, she ate a yellow school bus and thought it was a chip.
You momma is so fat she starved in *insert a supermarket*.
Loads more. I could just spam these all day long.