“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” A popular version involving a horse is:
 
“A horse walks into a bar and the barman says, ‘Why the long face?’”
 
A parody of this is:
 
“A fisherman walks into a bar holding a rather big fish. The barman asks, ‘Why the long plaice?’”
 
The punchline “Why the long plaice?” was posted on Facebook on June 2, 2010 and on Twitter on August 16, 2011.
 
         
Wikipedia: Plaice
Plaice is a common name used for a group of flatfish. There are four species in the group, the European, American, Alaskan, and scale-eye plaice.
 
Commercially, the most important plaice is the European. This is the principal commercial flatfish in Europe; it is also widely fished recreationally, has potential as an aquaculture species, and is kept as an aquarium fish. Also commercially important is the American plaice.
   
Facebook
Hi, I’m a girl. I bleed for a week and don’t die, just get angry. Fear me.
June 2, 2010 ·
Fisherman walks in to a bar after a good day’s haul. Barman says, “Why the long plaice?”
 
Twitter
Johnny Mac MBE‏
@_JohnnyMac_
A man walks into a pub with a stretched fish. The barman says “Why the long plaice ?”
3:51 PM - 16 Aug 2011
 
Twitter
Dandino‏
@dandino66
Horse walks into a bar carrying a huge fish. Barman: ‘Hey, why the long plaice?’
5:21 PM - 11 Nov 2011
 
Twitter
Tuna Fische‏
@drakestonehotel
Extended fish swims into a bar….Why the long plaice ?
5:22 AM - 28 Nov 2011
 
Twitter
Tim‏
@stig2112
Fisherman walks into a bar. The barman asks “Why the long plaice”.
8:23 AM - 30 Jul 2012
 
Twitter
PununciationDisorder‏
@ms_willow
A fisherman walked into a bar holding a rather big fish. The barman asks “Why the long plaice?”
6:42 AM - 16 Jan 2013
 
Twitter
Shit Jokes‏
@ShitJokes
Fisherman walks into a bar with his prize catch..
Barman, “Why the long plaice?”
3:47 PM - 20 Jul 2016
 
Twitter
Shit Jokes‏
@ShitJokes
Fisherman walks into a bar with his prize catch.
Barman, “Why the long plaice?”
11:57 AM - 13 May 2017