Yo mama is offended after reading these posts. Get some balls!

yo mama was so fat, and old, but then she died.

Yo' mama is so ugly that when she looks at goldfish crackers they stop smiling.

Since we're necroing this post, I guess I shall contribute.

Yo mama is so fat, she got more chins than a Chinese phonebook!

And a personal favorite: I don't need an IPod to listen to Dubstep, I can just slap yo mama's stomach! WUB WUB WUB xD

Yo mama is so ugly, when she looked into the mirror, the mirror got 7 years of bad luck

Yo mama is so ugly, that when she went to McDonalds and look at the Happy Meals, they turned into frowns.

Anon... you did the joke wrong... "Yo mama so fat she's got more Chins than a Hong Kong phone book." (Chinese refers to Mandarin, in which Chin is very rarely seen. However, it is common in Cantonese... Hong Kong... plus I kinda looked it up, haha).

for my additions:

Yo mama is so fat, she got arrested at the airport for ten pounds of crack

Your Mom is so slutty the free clinic sends her a christmas card.

Your Mom is so poor that her TV only has two channels: On and Off.

To you Chem/Phy nerds out there:

Your Mom conforms to Planck's law. The greater the frequency with which she screws, the more energetic she gets.

yo momma is so fat, last time she went to the beach i coulda sword i heard a whale singin 'We are family,I got all my sisters with me..."

yo Mama so stupid that she took a piece of paper and taped it on the t.v and called it paperview

Yo mama so ugly when she joined an ugly contest, they said "Sorry, no professionals."

^--- hahaha epic win

Yo mama's so ugly, that the MIA took her for a an alien

YO Mommas teeth are soo YELLOW when she closes her mouth her tummy glows