“If alcohol is a crutch, Jack Daniel’s is a wheelchair” was said by American actor and comedian Robin Williams at least by August 1990, when the joke was recorded in a newspaper.
 
The saying “alcohol is a crutch” has been cited in print since at least 1922. “We live in an imperfect world—imperfect largely because we have not yet gained the capacity to govern our own instincts,” said John McCurdy of Cornell Medical College, speaking at a 1922 meeting of the British Medical Association at Glasgow. “Alcohol is a crutch that man has discovered to help him with this disability.”
 
 
Wikipedia: Jack Daniel’s
Jack Daniel’s is a brand of sour mash Tennessee whiskey that is the highest selling American whiskey in the world. It is known for its square bottles and black label. It is produced in Lynchburg, Tennessee by the Jack Daniel Distillery, which has been owned by the Brown-Forman Corporation since 1956.
 
25 August 1922, Oakland (CA) Tribune, pg. 12, col. 2:
ALCOHOL HELD
“SOCIAL CRUTCH”
BY MEDICAL MEN
Meeting of British Physicians
Hear Liquor Asserted
As Beneficial.
LONDON, Aug, 25.—
(...)
ALCOHOL CRUTCH.
“We live in an imperfect world—imperfect largely because we have not yet gained the capacity to govern our own instincts. Alcohol is a crutch that man has discovered to help him with this disability.”
(Dr. John MacCurdy of Cornell Medical College—ed.)
 
17 August 1990, Worcester (MA) Telegram & Gazette, “Bottoms up is bad form on the slopes”:
Without question, drinking and skiing is a perilous preoccupation. As Robin Williams once observed: “If alcohol is a crutch, then Jack Daniel’s is a wheelchair.”
     
Google Groups: alt.tv.space-a-n-b
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1/10/97
>In my mind the best and most potent drink commonly available is Jack
Daniels Whiskey. Remember, if alcohol is a crutch the Jack Daniels is the
wheelchair!!<

 
Google Books
Final Betrayal:
A Novel of Suspense
By Elaine Taylor
New York, NY: iBooks
2005
Pg. 13:
But on their second date, after Rick downed five Jack Daniels straight-up, he laughed and told her, ‘if alcohol is a crutch, Jack Daniels is a wheelchair,’ yuck-yuck-yuck…”
   
Google Books
Ifferisms
By Mardy Grothe
New York, NY: HarperCollins Publishers
2009
Pg. 45:
If alcohol is a crutch, then Jack Daniel’s is the wheelchair.
Eight glasses and you forget the English language.
You just have one massive vowel movement.
ROBIN WILLIAMS
 
Twitter
Angi Roberts‏
@ShugerBooger
If alcohol is a crutch, Jack Daniels is a wheelchair.  Do a shot now.
8:59 PM - 4 Apr 09