A popular “yo mama” insult joke is:
 
“Yo mama is so stupid, she tried to put M&M’s in alphabetical order.”
 
Of course, they are all the letter “M.” The joke has been cited in print since at least 1993.
 
 
Wikipedia: M&M’s
M&M’s (styled as m&m’s) are “colorful button-shaped chocolates” produced by Mars, Incorporated. The candy shell, each of which has the letter “m” printed in lower case on one side, surrounds a filling which varies depending upon the variety of M&M’s. The original candy had a milk chocolate filling which, upon introducing other variations, was branded as the “plain” variety.
(...)
M&M’s originated in the United States in 1941, and are now sold in as many as 100 countries.
       
Google Books
On the Edge:
A history of poor black children and their American dreams
By Carl Husemoller Nightingale
New York, NY: BasicBooks
1993  
Pg. 27:
Your mom so dumb she try to put M&M’s in alphabetical order.
 
Google Books
Beer Games II:
The Exploitative Sequel
By Michael Balay
Memphis, TN: Mustang Publishing
1994
Pg. 26:
It’s basically trading witty insults, such as “You’re so stupid that you tried to put M&M’s in alphabetical order,” or “You’re so ugly that when you were born, the doctor slapped your mother.”
 
Google Groups: hk.talk.sex
Yo momma so stupid that she tried to put M&M’s in alphabetical order!
AaUnless
4/27/97
Testing
 
Google Groups: it.arti.cinema
Yo momma so stupid that she tried to put M&M’s in alphabetical order!
Associazione Culturale Mutation
11/9/98
Yo momma has a glass eye with a fish in it.
   
1 July 2004, Wisconsin State Journal (Madison, WI), “Nope, that’s not quite right,” pg. F1:
E-mailer Don checks in, with info about the guy who didn’t get it, the guy who:
(...)
* Tried to put M&M’s in alphabetical order.
 
Twitter 
Katherine Jenswold
‏@KattywinJ
Yo mooma so stupid she tried putting skittles in alphebetical order
6:55 PM - 16 Jun 2009
 
Twitter
Ayush Jha
‏@LEOMESSIandMORE
Yo momma is so stupid. ...: Yo momma is so stupid. She tried to put M&M’s in alphebetical order. http://url4.eu/MUuO
9:48 PM - 2 Sep 2009
 
Twitter
Yo Momma
‏@ohyomomma
OH: Yo momma is so dumb see tried to put M&M's in alphebetical order(: http://bit.ly/2N7Ywz
1:25 AM - 18 Oct 2009
 
YouTube
M&M’s in Alphabetical Order
spanishtaco wesely
Published on Jun 28, 2012
m&m’s in alphabetical order
 
Google Books
Yo Momma So Stupid Jokes 2
By Peter Crumpton
PeteyRF Creative
2015
Pg. ?:
YO MOMMA SO STUPID! that she tried to put M&M’s in alphabetical order!
 
Twitter
John Brookfield
‏@MeltHell
Yo momma is so stupid. She tried to put M&M’s in alphebetical order. http://fxmb.info/N8M3WQ  #jokes
2:42 AM - 19 Jan 2017