Ahhh...these remind me of my middle school bus rides to school. Here are some that I remember:
Yo mama is so fat that when she steps on a scale, it says "To Be Continued".
Yo Mama is so fat that when she went to the zoo, the elephants started throwing peanuts at her.
(warning: the following is not for people who get offended easily)
Yo mama is like a bowling ball. She gets picked up, fingered, thrown in the gutter, and still comes back for more.
Yo mama is so ugly that you have to tie a steak around her neck to get the dog to play with her.
Yo mama is so ugly that her pillow cries at night.
(warning: this is another that is not for people who get offended)
Yo mama is like a vacuum cleaner. She sucks, she blows, and she gets laid in the closet.
Yo mama is so fat that she uses I-95 as a slip n' slide.
I use to know so many more. In middle school, during our bus rides, we'd have "Yo Mama" contests. It's kinda like the battle of the words that you see in "8 Mile" except ours were with Yo Mama jokes. Sigh....it's amazing that I turned out normal.