“Don’t let your mouth write checks your body can’t cash”

“Don’t let your mouth write a check (or “checks”) your body (or “ass”) can’t cash” has been used in black English since at least the 1960s. Comedian Flip Wilson (1933-1998) used the line on television while performing in drag as the character “Geraldine.” However, a 1978 interview with Lou Rawls stating that he heard the phrase from his mother (see below) probably indicates that Flip Wilson wasn’t the first to use it.
 
The saying (recorded in print since at least 1966) means that one shouldn’t run one’s mouth, or one’s body/ass/behind might not be able to back it up.
 
     
Wikipedia: Flip Wilson
Clerow Wilson Jr., known professionally as Flip Wilson, (December 8, 1933 – November 25, 1998) was an American comedian and actor. Time magazine featured his image on their cover and named him “TV’s first black superstar”.
 
Dixie T-shirts
I’M ABOUT TO WRITE A CHECK YOUR ASS CAN’T CASH! T-shirt
   
Google Books
Norwood
By Charles Portis
New York, NY: Simon & Schuster
1966
Pg. 184:
“Don’t let your mouth write a check that your ass can’t cash, son.”
 
19 January 1972, Eugene (OR) Register-Guard, “Should City Officials Redly Jump Into Things This Way?” by Don Floyd, pg. B1, col. 3:
Quoting comedian Flip Wilson, Kelly said the venture materialized as a result of “letting your mouth write a check your body can’t cash.”
 
Google Books
Car: a novel
By Harry Crews
New York, NY: Morrow
1972
Pg. 60:
“Someday, if you’re not careful, you’ll write a check with your mouth that your ass can’t cash.”
       
Time magazine
Quick Cuts
Monday, Sep. 24, 1973
WHITE LIGHTNING concerns a good old boy named Gator McKluskey (Burt Reynolds) who is serving time in the Arkansas pen for messing around with illegal liquor.
(...)
Bridges, whenever he is not overburdened by the script’s Snuffy Smith dialogue (“Don’t write checks with your mouth your ass can’t cash”), can cut through to real depth
   
Google Books
2 March 1978, Jet magazine, “Lou Rawls Won’t Let Fame Spoil Him Again” by Bob Lucas, pg. 61, col. 1:
“There were those old ‘mother wit’ sayings she used to tell me, like, ‘Don’t let your mouth write a check your behind can’t cash.’ And when she would punish me: ‘I paid the cost to be the boss.’”
 
Google Books
Runnin’ Down Some Lines:
The language and culture of Black teenagers
By Edith A. Folb
Cambridge, MA: Harvard University Press
1980
Pg. 44:
Don ‘t let your mouth overload your ass or Don ‘t let your mouth write a check your ass can’t cash refers to provocative talk, talk that can often lead to a fight.
   
27 May 1985, Miami (FL) Herald, “Florida Routs Princeton, 14-4,” pg. 1D:
“There’s an old saying that Flip Wilson used when he played Geraldine. ‘Don’t let your mouth write a check your body can’t cash.’ ”
 
Google Books
African-American Proverbs in Context
By Anand Prahlad
Jackson, MS: University Press of Mississippi
1996
Pg. 239:
Don’t let your mouth write a check that your behind can’t cash.
Infmnt: Maxine Hudnall, 35, clerk, Oakland, California, 11-17-71. From Oakland Army Base, 1970.
Usage: “My informant told me that someone in her office told this to another worker that had a tendency to overdo everything.”
Pg. 240:
Usage: Don’t let your mouth write a ticket your ass can’t cash. Don’t take a position that you can’t defend.”
Infmnt: Emma Gordan, 69, Berkeley, California, 10-71. Berkeley Archives.
Usage: “Your mouth is going to cause you a check, your ass is going to have a chase.” Used often by adults to children, as a way of saying “If you talk too much you may not be able to talk your way out of the situation.” Used by peers on the verge of going from a verbal fight to a physical one. Means: Don’t make statements that you cannot physically back up.