“A guy walks into a bar...” is a typical form of what has been called the “bar joke.” A last man on earth version is:

“The last man on earth walks into a bar and says, ‘Drink, I’d like another bartender.’”

The joke is from the novel The Rule of Four (2004) by Ian Caldwell and Dustin Thomason.


Google Books
The Rule of Four:
A Novel
By Ian Caldwell and Dustin Thomason
New York, NY: The Dial Press
2004
Pg. 304:
“The last man on earth walks into a bar,” he murmurs. “What does he say?”

Paul turns his head toward the window, but doesn’t offer the punch line. We both know what the last man on earth says. He looks into his beer, lonely and besotted, and says, “Drink, I’d like another bartender.”

WENCHIE LOSTELF
TUESDAY, AUGUST 15, 2006
The last man on Earth walks into a bar, What does he say?
Drink, I’d like another bartender.
POSTED BY WENCHIE LOSTELF AT 02:54

Twitter
rachelropp
@rachelropp
So the last man on earth walks into a bar and says, “Drink, I’d like another bartender”....
3:56 PM · Jan 25, 2009·Twitter Web Client

Twitter
Fransco
@fransco
“The last man on Earth walks into a bar and says drink, I’d like another bartender.” ~ The Rule of Four
5:56 PM · Jun 4, 2013·Twitter for iPhone

Twitter
((( 1/f ))) フェダシング / फेडसिंह
@fadesingh
The last man on earth walks into a bar. He looks into his beer and says, “Drink, I’d like another bartender.”
4:24 AM · May 9, 2015·Twitter Web Client

Twitter
Scotty The Body
@ScottRotPotSnot
“The last man on earth walks into a bar. What does he say?
‘Drink, I’d like another bartender.’”
Sometimes when you read good novels you learn a good riddle.
12:15 PM · Oct 29, 2018·Twitter for Android

Twitter
robo bim
@robocryptid
another:
the last man on earth walks into a bar
he gets himself a whiskey
he says, “drink, I need another bartender”
10:53 PM · Dec 25, 2018·Twitter for iPhone