Your mom's like a pool table, balls go in and out.

yo mama so fat she got in the car and made it a low rider.

Your momma's so dumb they told her it was chilly outside, she went and got a bowl.

Also, just for the record, a your mom variation is one of the perfect responses to almost any question.

Q: What time is it?
A: Half past your mom.

It works for most anything, and most of the stuff it doesn't work on, very carefully works for.

Yo mama so fat, that when she crossed the TV, I missed the whole Vikings-Saints game.

Yo mama so fat, that she has citizenships in 4 different countries.

Yo mama so fat, she bumped Jay back to the Tonight show.

I remember you saying that a couple years back.

OT: Yo momma so fat she wore high heels outside and struck oil.

Yo momma is so fat, after sex I rolled over twice and I was still on the bitch!

Yo mama so stupid she sold her car for gas money.
Yo mama so fat Spain tried to claim her as the new world.
Yo mama so fat that when she was gong to McDonald's, she tripped over Wendy's and landed on Burger King.

The classics never die. 

Quit talking about my mama!!! I've reported all of you.

your mom reported you.