A drinking rhyme was printed in The Berkshire Evening Eagle (Pittsfield, MA) on March 18, 1916:
   
“I know many reasons for drinking,
And one has just entered my head—
If a man can’t drink while he’s living
How in hell can he drink when he’s dead?”
 
The rhyme wasn’t printed during the Prohibition years, but was printed in The Spur (New York, NY) in slightly different form in June 1936:
   
“There are many good reasons for drinking,
One has just entered my head,
If a man doesn’t drink when he’s living
How the hell can he drink when he’s dead?”
 
The rhyme is often associated with drinking on St. Patrick’s Day.
             
   
Newspapers.com
18 March 1916, The Berkshire Evening Eagle (Pittsfield, MA), “The Note Book,” pg. 4, col. 3:
REVIVAL OF AN OLD PUZZLE.
I know many reasons for drinking,
And one has just entered my head—
If a man can’t drink while he’s living
How in hell can he drink when he’s dead?
   
June 1936, The Spur (New York, NY), “Forty Days a Seaman” by Bradish Johnson, Jr., pg. 86, col. 3:
“There are many good reasons for drinking,
One has just entered my head,
If a man doesn’t drink when he’s living
How the hell can he drink when he’s dead?”
 
Newspapers.com
29 April 1937, Thomson (IL) Review, pg. 4, col. 4:
There’s many good reasons for drinking.
A new one just entered my head.
If you don’t drink while you’re living; how the heck are you going to drink when you’e dead?
 
Old Fulton NY Post Cards
10 October 1942, Irish American Advocate (New York, NY), pg. 7, col. 6:
“There are many good reasons for drinking,
One has just entered my head,
If a man doesn’t when he’s living
How the H—- can he drink when he’s dead.”
Mike (Tipp) Ladrigan.
 
Newspapers.com
26 September 1948, Hilo (HI) Tribune-Herald, “Koko-Nuts” by J. B. Dixon, pg. 4, col. 3:
There are many good reasons for drinking,
And one has just entered my head,
If a man doesn’t drink when he’s living
How the heck can he drink when he’s dead?
—Contributed by M.I.
 
22 July 1950, Chicago (IL) Defender, Langston Hughes column, pg. 6, col. 6:
“Now I will say you a toast:
 
If you want a good reason for drinking, daddy—
A mighty fine reason just entered my head—
If a man don’t drink when he’s living
How can he drink when he’s dead?”
 
Google Books
Eating and Drinking:
An Anthology for Epicures
Compiled by P. J. Hunt
London, UK: Ebury Press
1961
Pg. 26:
There are several reasons for drinking
And one has just entered my head;
If a man cannot drink when he’s living
How the Hell can he drink when he’s dead.
Anon.
 
Newspapers.com
17 November 1962, Oneonta (NY) Star, “Lighter Side” With Gene Brown, pg. 4, col. 8:
No Post Mortem Martini
There are several reasons for drinking,
And one has just entered my head,
If a man doesn’t drink when he’s living
How the hell can he drink when he’s dead?
   
Google Books
The Life and Works of Mr. Anonymous
By Willard R. Espy
New York, NY: Hawthorn Books
1977
Pg. 76:
Uncle Allie unscrewed his flask-cap again, swallowed, and recited:
 
There are several reasons for drinking,
And one has just entered my head;
If a man cannot drink when he’s living
How the hell can he drink when he’s dead?
 
Google Books
Bill Wannan’s Folklore of the Australian Pub
By Bill Wannan
South Melbourne, Victoria: Macmillan
1972
Pg. 118:
There are many good reasons for drinking — And one has just entered my head: If a man doesn’t drink when he’s living, How the hell can he drink when he’s dead!
       
Google Groups: alt.quotations
Reasons for drinking
Toby Nieboer
4/26/93
From a souvenir/trinket beer mug my grandfather has:
 
I have a few good reasons for drinking
And one has just entered my head
If a man can’t drink when he’s living
How the hell can he drink when he’s dead?
 
Twitter
PaddyO
@OhPaddyO
Replying to @OhPaddyO and @Sextibles
And of course
“There are many good reasons for drinking,
One has just entered my head-
If a man doesn’t drink when he’s living,
How the hell can he drink when he’s dead?”
8:16 PM · Feb 21, 2019·Twitter for Android
 
Twitter
Someone
@Leonoh_
There are many good reasons forma drinking, one has just entered my head.
If a man doesn’t drink when he’s living, how the hell can he drink when he’s dead?
#hippiebirthday
GIF
2:14 PM · Jan 11, 2020·Twitter for Android