A popular “yo mama” insult “fat joke” is:
 
“The earth used to be flat…until they buried yo mama.”
 
“Yo mamas so fat, the earth was flat until somebody buried her” was posted on Twitter on November 2, 2011. “The earth used to be flat, until yo mamma was buried” was posted on Twitter on February 23, 2014. “The Earth used to be flat, but then they buried yo mama” was posted on Reddit—Jokes on February 9, 2018.
   
   
Wikipedia: Flat Earth Society
The Flat Earth Society (also known as the International Flat Earth Society or the International Flat Earth Research Society) is an organization that seeks to further the belief that the Earth is flat instead of an oblate spheroid. The modern organization was founded by Englishman Samuel Shenton in 1956 and was later led by Charles K. Johnson, who based the organization in his home in Lancaster, California. The formal society was inactive after Johnson’s death in 2001 but was resurrected in 2004 by its new president Daniel Shenton.
         
Twitter
▲‏
@commonfake
Yo mamas so fat, the earth was flat until somebody buried her.
6:26 AM - 2 Nov 2011
 
Twitter
Jimena del Valle‏
@jimedelv
The earth used to be flat, until yo mamma was buried.
10:23 PM - 23 Feb 2014
     
Twitter
Da’Bau5‏
@Lee_Jay_17
The earth was flat….......Until they buried your mother 😉 #Broken
5:41 AM - 25 Feb 2014
 
Twitter
Brenden‏
@BrendenElwood
The Earth used to be flat….. until Yo Mamma was buried
7:59 PM - 25 Feb 2014
     
Twitter
Your Mom‏
@MamaComebacks
Your mama’s so fat that at first the earth was flat until your mom was buried
5:42 PM - 17 Mar 2014
 
Twitter
dead‏
@KiteBallet
The earth used to be flat until they buried yo mamma.
6:41 AM - 24 Sep 2016
   
Twitter
Bryan Soong‏
@BryanSoongg
The earth was flat….. until YO MAMA GOT BURIED
5:21 AM - 5 Mar 2017
   
Twitter
🅝🅞🅑🅛🅔‏
@KeishaLanceVers
At first the earth was flat, then they buried yo mama!
8:31 AM - 19 Jan 2018
 
Reddit—Jokes
The Earth used to be flat,
submitted February 9, 2018 by aFullmetalTaco
but then they buried yo mama.