“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” One popular joke is:
 
“A skeleton walks into a bar and says, ‘Bartender, give me a beer and a mop.’”
 
The joke has been cited in print since at least 1996.
 
         
A Prairie Home Companion with Garrison Keillor
Jokes
Saturday, April 27, 1996
(...)
This skeleton walks into a bar and says give me a beer and give me a mop.
 
Google Books
Hardcore Visual Basic
BY Bruce McKinney
Redmond, WA: Microsoft Press
1997      
Pg. 486:
A skeleton walks into a bar and says, “Bartender, give me a beer and a mop.”

Google News Archive
19 November 1997, Spartanburg (SC) Herald-Journal, “The Stroller” by Lou Parris, Pg. B3, col. 1:
The skeleton walks into a bar and says, “Give me a beer and a mop.” .
 
Google Books
The New York City Bartender’s Joke Book
By Jimmy Pritchard
New York, NY: Warner Books, Inc.
2002
Pg. ?:
A skeleton walks into a bar, walks up to the bartender and says, “Give me a beer and a mop.”
 
Twitter
Dreaming Dragon
‏@TheDragon__
A Skeleton walks into a bar, asks for a beer… and a mop.
3:55 PM - 25 Sep 2007
 
YouTube
Funny joke | A skeleton walks into a bar | Rudolf Von Strudel
Sam Spiegel
Published on Jun 25, 2012
http://rudolfvonstrudel.com
A skeleton walks into a bar, a funny joke told by Rudolf Von Strudel
Rudolf Von Strudel is a famous movie star and a joker from Eastern Europe
 
Twitter
200 Degrees Cafe
‏@200DegreesCafe
A skeleton walks into a bar and says, ‘I’d like a beer and a mop…’ #TellAnOldJokeDay Got one for us?
5:24 AM - 24 Jul 2015