“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” There are several jokes about two or three men walking into a bar and ducking (or not ducking). The following joke is from 1990:
 
“These two guys walk into a bar,,  You think that the second one would have ducked…...”
     
This joke is from 1993:
 
“Three men walking down the street, two walk into a bar - the third ducked.”
 
“Two blondes walk into a building. You’d think one of them would have seen it” is a variation on the bar joke.
   
 
Google Groups: alt.stupidity
Knock Knock
Liam G Curry
11/28/90
In article

, weinrich@orchestr>
>  “A man walks into a bar and says ‘ouch!’”
 
These two guys walk into a bar,,  You think that the second one would have ducked…...
 
Google Groups: rec.humor
bar joke    
Wally Thomson
2/4/93
(...)
Three men walking down the street, two walk into a bar - the third ducked.     
   
Google Groups: rec.humor
a shorter, funnier joke!!
Alan Wilson
12/10/93
(...)
Two men walk into a bar. You’d think the second one would have seen it.
 
JANINE O. JOHN
12/16/93
(...)
Two men walk into a bar… the third one ducked…
 
Google Groups: rec.puzzles
A Man Walks into a Bar
Dana Carroll
11/15/94
(...)
Three men walk into a bar.  You’d think one of them would have ducked!
 
Google Groups: rec.humor
Horse walks into a bar…...
Wesley F Wright
2/23/95
.(JavaScript must be enabled to view this email address) (John Wiswell) wrote:
>Horse walks into a bar
>
>Bartender says….” Why the long face?”
 
Two guys walk into a bar.
The third one ducked.
 
Google Groups: rec.humor
Two men walk into a bar…
.(JavaScript must be enabled to view this email address)
10/24/96
Two men walk in to a bar.
You’d think the other one would have ducked…
 
Google Groups: rec.humor
Three guys walk into a bar…
King of All Windbags
1/30/97
...the fourth one ducked.
 
Google Groups: alt.tasteless.jokes
2 men walk into a bar
paul r morin
5/24/97
2 men walked into a bar,
second one should’ve ducked!
 
Google Books
Funny Boy Takes on the Chitchatting Cheeses from Chattanooga
By Don Gutman
New York, NY: Hyperion Book
2000    
Pg. 28:
“Okay, these two guys walk into a bar. You’d think the second one would have ducked.”
 
Google Books
Guy Walks Into A Bar…:
501 Bar Jokes, Stories, Anecdotes, Quips, Quotes, Riddles and Wisecracks
By Michael Lewis
New York, NY: Black Dog & Leventhal Publishers, Inc.
2005
Two guys walk into a bar. You d think the second guy would have ducked.
 
Google Books
Waiting for War
By James Brokaw, 3rd
Hedgie Press
2011
Pg. ?:
“Like this: Two men walk into a bar. You’d think the second one would have ducked.”
 
Twitter
Smike
‏@SmikeTV
Three men walk into a bar. You’d think the third man would’ve ducked.
1:12 PM - 13 Oct 2015
 
Twitter
David Aronoff
‏@dba
Two men walk into a bar. The third one ducked. #badcleanjokes
12:58 PM - 24 Oct 2015