“Yo mama is so ugly, she can make yogurt just by staring at a glass of milk”

A popular “yo mama” insult joke is:
 
“Yo mama is so ugly, she can make yogurt just by staring at a glass of milk for an hour.”
 
The joke has been cited in print since at least 2000.
 
     
Google Books
1001 Really Stupid Jokes
By Mike Phillips
London: Constable & Robinson Ltd
2000
Pg. ?:
Did you hear about the woman who was so ugly she could make yogurt by staring at a pint of milk for an hour?
   
Twitter
sad jones‏
@RaynePassion
Did you hear about the woman who was so ugly she could make yogurt just by staring at a glass of milk for an hour?
1:34 PM - 11 Apr 2010
 
Twitter
#TrueHogsClub‏
@Sourdough87
#Yomama so ugly she can make yogurt just by looking at a glass of milk
5:16 PM - 23 Jan 2012
 
Twitter
GET LOLIFIED!‏
@TheLOLWorld
JOKE:
      Yo Momma’s so ugly, she can make yogurt by just staring at a glass of milk for a couple of hours.
… http://ift.tt/1Jh6qxV
2:04 AM - 19 Aug 2015
 
Twitter
John Brookfield‏
@MeltHell
Yo Momma’s so ugly, she can make yogurt by just staring at a glass of milk for a couple of hours. http://fxmb.info/N0c7wr  #jokes
10:13 PM - 30 Dec 2016
   
Twitter
KINGCurtisRaye™‏
@KINGCurtisRaye
Yo Momma so ugly, she can make yogurt by just staring at a glass of milk for a couple of hours.. 😂😂😂😂💀💀💀🏃🏃🏃🏃🏃 #🌽jokes
11:02 PM - 17 Mar 2017