“Lactose intolerant” is sometimes jocularly called “black toast intolerant.”
   
“My Daddy can’t eat that toast, he is black toast intolerant” was posted on the newsgroup alt.humor.puns on March 15, 2000. “My doctor advised me against eating very burnt bread . I am black toast intolerant” was posted on Twitter by Joe Cluxton on July 18, 2021. “What do you call someone who’s allergic to burnt bread? Black-toast intolerant” was posted on Reddit—Dadjokes on May 1, 2022.
   
“Blacktoast-Intolerant” was entered in the Urban Dictionary on October 6, 2008. “Black toast intolerant” was entered in the Urban Dictionary on June 3, 2021.
     
“Lack Toast And Taller Ant or Lack Toast” is a similar joke,
       
     
Wikipedia: Lactose intolerance
Lactose intolerance is the inability of adults and children to digest lactose, a sugar found in milk and to a lesser extent dairy products, causing side effects. It is due to a lactase deficiency, or hypolactasia. In some (rare) cases, individuals have congenital alactasia, a total absence of lactase caused by a genetic defect, which prevents them from being able to digest lactose from infancy.
     
The Eggcorn Database
lactose » lack toast
Chiefly in:  lack toast intolerant , lack toast and tolerant
         
Google Groups: alt.humor.puns
Lactose Intolerance
Stan Kegel
Mar 15, 2000, 3:00:00 AM
A scientist found, to his great surprise, that he was lactose intolerant (unable to digest milk sugar). At dinner that night with his two young daughters (age 9 and 4 years), he mentioned that he had found out that he was lactose intolerant and tried to explain to them what that meant.
 
A couple of months later, he took the kids to a local restaurant for a quick breakfast before shopping. The place was very busy but the quality of the food and service were obviously not up to par. When they finally got their breakfast, his youngest daughter took a look at her father’s omelet and burnt toast and declared very loudly to the waitress “My Daddy can’t eat that toast, he is black toast intolerant.”
 
Needless to say, after a moment’s silence, the whole restaurant burst into laughter. (By Terry Galen)
   
Newspapers.com
25 July 2000, Fort Worth (TX) Star-Telegram, “Quotable Kids,” pg. 10E, col. 6:
One evening, my 5-year-old daughter overheard my husband and me discussing the possibility that she may be lactose intolerant. Kids are all ears, because the next morning, over a breakfast of buttered toast, she announced to my oldest daughter: “Sissy, mama thinks that I may be black toast intolerant!” I had to agree with her, and said I didn’t much care for it, either.
—Laura Abbott, Fort Worth
 
Google Groups: alt.humor.puns
“Puns of the Weak” 11/24/00          
Stan Kegel
Nov 25, 2000, 3:00:00 AM
Hauke Reddmann wrote:
> Stan Kegel wrote:
> > I hate guys with foot fetishes. I’m lick toes intolerant. (Cynthia MacGregor)
> Even worse - amputee fetish. I’m lack toes intolerant.
 
I’m a nervous wreck if I don’t get my morning toast.
I’m lack toast intolerant.
But I must have my bread toasted lightly.
I’m black toast intolerant.
 
Google Groups: alt.humor.puns
Puns of the Weak 8/10/01
Stan Kegel
Aug 11, 2001, 1:27:20 AM
(...)
A few months ago my five year old son informed us that he thought he was “black toast intolerant.” (Michael Brunelle)
     
Google Groups: alt.humor.puns
Puns of the Weak 1-31-03
Stan Kegel
Jan 31, 2003, 10:03:19 PM
(...)
One morning I handed my 8 year old her toast which was a little on the dark side. She said, “I can’t eat that, I’m black toast intolerant.”
(Funny Kids)
     
Google Groups: alt.humor.jewish
Groaners of the Weak 01-25-05
Stan Kegel
Jan 21, 2005, 2:29:07 PM
(...)
A man took the kids to a local restaurant for a quick breakfast before shopping. The place was very busy, but the quality of the food and service were obviously not up to par. When they finally got their breakfast, his youngest daughter took a look at her father’s omelet and burnt toast and declared very loudly to the waitress “My Daddy can’t eat that toast, he is black toast intolerant.”
       
Urban Dictionary
Blacktoast-Intolerant
A condition were burnt toast causes the tear ducts to explode and you cry.
I was eating toast when Blacktoast-Intolerant kicked in and I bawled bro.
by JMRILEY October 6, 2008
 
Twitter
licketySplitAUS
@licketySplitAUS
My son was at breakfast one morning and refuses to eat his breakfast. I ask why? He says I’m black toast intolerant.
10:08 PM · Oct 30, 2008·Twitter Web Client
 
Reddit—Jokes
Posted by u/[deleted] May 8, 2010
What do you call someone who really hates burnt bread?
Black-toast intolerant!
   
Reddit—Dadjokes
Posted by u/[deleted] April 30, 2015
My daughter told me not to make her toast too dark at breakfast this morning…
“Why?” I asked, “Are you black-toast intolerant?”
     
Reddit—Jokes
Posted by u/USAneedsAJohnson January 28, 2017
A toast!
Had to throw away my toaster because it kept burning my toast. I guess you could say I’m black toast intolerant.
 
Reddit—Punny
Posted by u/HELLO_I_HAVE_A_PENIS February 9, 2017
I burnt a piece of bread in the toaster and now I can’t eat it…
Not because of the taste but because I’m black toast intolerant.
 
Reddit—Puns
Posted byu/Punsville April 12, 2017
Food Puns
(...)     
Did you hear the one about the woman who threw her toaster away because it kept burning the bread? She was black toast intolerant.
 
Reddit—Puns
Posted by u/Punsville April 18, 2017
Bread Puns
(...)
45- The young lady threw her toaster in the trash because she was black-toast intolerant.
     
Reddit—Dadjokes
Posted by u/st-huck May 2, 2018
I accidentally burnt some toast this morning
I threw it away because I am black toast intolerant.
     
Reddit—Dadjokes
Posted by u/porichoygupto July 31, 2018
Nurse: Are you allergic to anything? Dad: Burnt bread.
Nurse: You are allergic to burnt bread?
Dad: Yes, I’m black toast intolerant.
 
Reddit—Jokes
Posted by u/live4lifelegit October 3, 2018
I have a medical condition that means I can die if I have burnt bread..
I am black toast intolerant
 
Reddit—Dadjokes
Posted by u/FreakyStarrbies January 24, 2019
I yelled at the waitress for burning my toast. I told her I will not stand for it!
I guess you could say I’m black toast intolerant.
     
Reddit—Dadjokes
Posted by u/MF62SW May 12, 2019
What do you call burnt bread that can’t consume dairy?
Black toast intolerant
   
Urban Dictionary
Black toast intolerant
It’s actually “lactose intolerant”. And why tf would it be “black toast”? You know what LACTOSE intolerance is, what does burnt toast have to do with the inability to digest dairy? You’re letting me down man.
(...)
by Ronald k chump June 3, 2021
   
Twitter
Joe Cluxton
@Castletonian
Replying to @LindaRo03126195
Good.  My doctor advised me against eating very burnt bread . I am black toast intolerant.
3:12 PM · Jul 18, 2021 from Kildare, Ireland·Twitter for iPhone
 
Reddit—Puns
Posted by u/DinglebarryHandpump October 19, 2021
I can’t stand burned bread
I am black toast intolerant
 
boredpanda
April 2022
153 Absolutely Bread-tastic Bread Puns
Aivaras Kaziukonis and Justė Kairytė - Barkauskienė
(...)
#43
My doctor advised me against eating burnt toast. I am black toast intolerant.
 
Reddit—Dadjokes
Posted by u/Stewpot97 May 1, 2022
What do you call someone who’s allergic to burnt bread?
Black-toast intolerant
 
LaffGaff
Bread Allergy
May 8, 2022 by laffgaff
What do you call someone who’s allergic to burnt bread?
Black toast intolerant.