A popular “yo mama” insult “fat joke” is:

“Yo mama is so fat, people jog around her for exercise.”

The joke was posted on the newsgroup rec.humor on September 7, 1994.


Google Groups: rec.humor
Yo momma Jokes list
Chris Litchfield
9/7/94
(...)
Yo momma so fat people jog around her for exercise

Google Books
Mo’ Yo’ Mama!:
Bust-o-Pedia
By Snap C. Pop.
New York, NY: Berkley Books
1996
Pg. ?:
Yo’ Mama’s so fat, people jog around her for exercise.

Google Groups: hk.talk.sex
Yo momma so fat people jog around her for exercise
AAAtest
4/27/97
Testing

27 August 2004, Charleston (WV) Gazette, “Geez, Bob. Chill out on the hissy fits over Abercrombie’s T-shirts” by Susanna Rodell, pg. 4A:
Didn’t you learn anything in elementary school, Bob? Remember when the kids used to tease you? It happens to every kid at some point. What did they say? Man, you got some big ears. Can you fly with those things? Or maybe the classic: Yo mama. Yo mama so dumb, you have to dig for her IQ! .... Yo mama so fat, people jog around her for exercise!

7 July 2007, The Gold Coast Bulletin (Southport, Queensland), “At Our Wit’s End,” pg. 29:
However, `yo mama’ jokes are primarily used as `snaps’ or one- liners:

* Yo mama so fat people jog around her for exercise.

Google Books
Bob and Brenda’s Joke Book
By Paul Gwilliam
Lulu Publishing (Lulu.com)
2014
Pg. ?:
Yo mama is so fat people jog around her for exercise.

Google Books
A Prairie Home Companion
Pretty Good Joke Book (6th Edition)
Introduced by Garrison Keillor
Prince Frederick, MD: HighBridge, a division of Recorded Books
2015
Pg. ?:
Yo’ mama is so fat, people jog around her for exercise.