The past tense of “fit” is not “fat,” but there are jokes. Often “sit” and “sat” are compared.
 
“And is ‘fat’ the past tense of ‘fit’?” was posted on the newsgroup alt.usage.english on September 12, 2000. “The past tense of ‘fit’ should be ‘fat’” was posted on Twitter by Bill Pellowe on May 25, 2008.
 
“If the past tense of sit is sat… why is the past tense of Fit not Fat???” was posted on Twitter by Ahh! Photography on August 13, 2009. “‘Sat’ is the past tense of ‘Sit’ which means ‘Fat’ should be the past tense of ‘Fit’” was posted on Reddit—Showerthoughts on September 21, 2014. “If ‘sat’ is the past tense of the word ‘sit’, then the past tense of ‘fit’ should be ‘fat’” was posted on Reddit—Showerthoughts on March 23, 2015.
 
“The past tense of ‘fit’ is ‘fat’?” was posted on Twitter by Violetta Polevodina on August 23, 2010. “The past tense of ‘fit’ is ‘fat’” was posted on Twitter by Josh Long on October 17, 2010. “The past tense of fit is fat” was posted on Reddit—Showerthoughts on September 26, 2018.
     
         
Google Groups: alt.usage.english
Past Tense of sneak?
Orne Batmagoo
9/12/00
(...)
>>      And is “fat” the past tense of “fit”?
>
> You’ve got it backwards!  “Fat” is the future tense of “fit”.
 
As in:  Will Joshua fat the battle of Jericho?
   
25 October 2006, Daily Breeze (Torrance, CA), “Genuine, Loving and Thoughtful” by Shirley Hsu, pg. A1:
There were jokes only a teammate could truly appreciate—of nicknames and pranks pulled during travel games. They told of Blankinship’s signature soccer move, the “Blankinship crossover- fake,” and of how Blankinship once cracked up her teammates when she insisted that “fat” was the correct past tense of “fit.”
   
Twitter
Bill Pellowe
@billpellowe
The past tense of “fit” should be “fat”
3:53 PM · May 25, 2008·Twitter Web Client
   
Twitter
Ryan S.
@conedude13
In a correct world, the past tense of fit would be fat. FIX IT!!
8:33 AM · Nov 16, 2008·Twitter Web Client
 
Twitter
EFDF
@WatchEFDF
FAT; the past tense of ‘FIT’
8:57 PM · Jan 18, 2009·Twitter Web Client
   
Twitter
Moniker
@Moni2332
I still think the past tense of “Fit” should be “Fat” just like “Shit” and “Shat”...
12:40 PM · Jul 24, 2009·Twitter Web Client
 
Twitter
Ahh! Photography
@AhhPhotography
If the past tense of sit is sat… why is the past tense of Fit not Fat???
9:55 PM · Aug 13, 2009·Twitter Web Client
     
Twitter
Kevin F. Smith
@kefrith
Replying to @AhhPhotography
@AhhPhotography In many cases, the past tense of fit IS fat!
10:02 PM · Aug 13, 2009·Twitter Web Client
     
Twitter
Penny Proud
@iamchelseaiam
If sat is the past tense of sit,why isn’t fat the past tense of fit?
11:35 PM · Oct 24, 2009·Twitter SMS
   
Twitter
Youtube ThatGuyTyke
@Tyke_Designz
#dumbquestions If the past tense of sit is sat… why is the past tense of Fit not Fat
11:30 AM · Nov 13, 2009·Twitter Web Client
 
Twitter
Violetta Polevodina
@WontonSan
The past tense of “fit” is “fat”?
3:49 AM · Aug 23, 2010·ÜberSocialOrig
   
Twitter
Josh Long (龙之春, जोश, Джош Лонг, جوش لونق)
@starbuxman
The past tense of “fit” is “fat.”
8:06 PM · Oct 17, 2010·Twitter for iPhone
   
Twitter
Tyler
@tarpin158
The past tense of fit is fat
11:14 AM · Mar 20, 2011·DROID
 
Reddit—Showerthoughts
Posted by u/Saikou0taku September 21, 2014
“Sat” is the past tense of “Sit” which means “Fat” should be the past tense of “Fit”
   
Twitter
JD Roberto
@jdroberto
“Sat” is the past tense of “Sit” which makes sense, cause if you think about it “Fat” should be the past tense of “Fit”
2:30 PM · Sep 27, 2014·Hootsuite
 
Reddit—ShittyAskScience
Posted by u/wOlfLisK December 19, 2014
If the past tense of sit is sat and the past tense of kit is cat, why is the past tense of fit not fat? (self.shittyaskscience)
Engrish hard :(.
 
Reddit—Showerthoughts
Posted by u/Bostonkid95 March 23, 2015
If ‘sat’ is the past tense of the word ‘sit’, then the past tense of ‘fit’ should be ‘fat’.
     
Google Books
The Curmudgeon’s Dictionary
By William Soisson
Xlibris (Xlibris.com)
2016
Pg. ?:
Fat, adj.: Past tense of fit.
 
Reddit—Showerthoughts
Posted by u/jedi3579 April 3, 2018
If sat is the past tense of sit, then fat is the past tense of fit.
     
Reddit—Showerthoughts
Posted by u/firelord_airo September 26, 2018
The past tense of fit is fat
   
Twitter
Mother Of Sarcasm
@SarcasmMother
The past tense of fit is fat.
1:57 PM · Sep 27, 2018·Twitter Web App
 
Facebook
The criminal Potato
September 29, 2018 ·
The past tense of fit is fat.
   
Twitter
Talk To The Hatter
@Talk_To_The_Hat
If sat is the past tense of sit, then fat is the past tense of fit.
7:26 PM · Mar 29, 2019·Twitter Web Client
 
Twitter
Talk To The Hatter
@Talk_To_The_Hat
If sat is the past tense of sit, then fat is the past tense of fit.
1:18 PM · Mar 7, 2020·Twitter Web App