Yo mama’s so fat that the fire marshal made her favorite restaurant put up a sign that says, “maximum occupancy: 200 people or Yo Mama.”
Reminds me of David Niven once commenting on Terry Thomas: “He could eat an apple through a tennis racket.”
And by the way, Yo’ Mama is like a birthday cake. Everybody gets a piece.
Yo Mama’s so busted, if she solved a crime, she would be rewarded with a Scooby-Snack.
I saw yo mamma in the bank today. I called her a two-bit ho and she got so mad, she hit me over the head with a bag of quarters.
Yo mamma’s glasses be so thick that when she looks at a map, she can see people waving at her.
And yo daddy’s so fat they use his belt as a first down chain at the football stadium.
Yo momma’s so fat the back of her neck looks like a pack of hot dogs.
Yo mamma so fat, it takes 2 Borg cubes to assimilate her
Yo mamma so fat, they have to put another notch in the Van Allen belt
And more erudite:
Yo mamma so fat, when she sat on a rainbow, it turned to Skittles
Yo mama so fat, when people yell “Hey Kool-Aid”, she come bustin’ through the wall.
Yo mama’s so dumb she was driving me to the airport and when she saw the sign that said “Airport - Left” she turned around and went home.
Yo mama’s so poor, when I asked her why she was kicking a can down the street she said “I’m Movin”
Yo mama’s so fat she offers guided donkey tours down her butt crack
Yo mama’s so stank Tacoma complained
Yo momma such a stupid ho, she named all 14 of her kids <your first name> so she can call of you all at one time. If she only wants one to come, she uses their last names.
Yo momma so poor that, at Thanksgiving, she took you to KFC to lick other peoples fingers.
Yo momma such a drunk that she took a blood test; it came back AB positive and 28 proof.
Leuzinger High School in Lawndale CA, early eighties. I used these almost daily to avoid physical fights. If you out-dissed somebody, it was wrong to beat up the winner.
Peace - DESK
Yo mamas like a race car, burns up 4 rubbers every time she goes out.
Yo mama is so boring, I can’t make no jokes about her!
I cannot comment on your mother for in my country cows are sacred.
Well your mommas must not have raised you right, because these are not nice things to say.
(Stolen from 30 Rock)
Yo momma so fat, her Patronus is a pie.
Yo mama’s so fat she jumped in the air and got stuck.
A series of Shakespearean and literary Yo Mama jokes from another thread.
I used to love telling these in school, even before I knew what they really meant.
Yo Momma’s like a TV set, a 3 year old can turn her on
Yo Momma’s like 7-Eleven, open 24 hours a day
Yo Momma’s like the transcontinental railroad, she’s been laid across the country
Yo Momma’s like a door knob, every one gets a turn
Yo Momma’s like a bus, people get on and off her all day
Yo Momma’s like a stop sign, you see her at every corner
Yo Momma’s like a gun, one cock and she blows
Yo Momma’s like a rooster, but instead of “Cock-a-doodle-doo”, she goes “Any cock will do”
Yo Momma’s so ugly, she has to wear a pork chop to get the dog to play with her.
My favorite from Eric Cartman: Your momma’s so poor she walks down the street with one shoe on, and when people ask her if she lost one she says, “No, I found one.”
If ugly was bricks, yo Momma would be the projects.
Yo Momma’s breath so stank, I had to hang up the phone.
Yo Mama is so poor that she is in at least the third generation of unemployment and public dependency, trapped from birth in an impoverished, socially dysfunctional and dangerous inner-city environment, poorly and meagerly educated at underfunded public schools, forced to raise her several children without the help or presence of their several fathers, dooming herself and you and in all probability your own children and grandchildren, should you survive the mean streets long enough to reproduce, to squalid, useless lives of want, ignorance and desperation.
Oooooh, SNAP! 
“Any cock’ll do.”