“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” “A dyslexic man walks into a bra” is a joke about a joke, or a “meta-joke.”
 
“So this dyslexic walks into a bra” was cited in print in 2001 and “Dyslexic man walks into a bra….” was cited in 2002.
 
“A drunk dyslexic wanks into a jar” is another “dyslexic” joke.
 
   
Wikipedia: Meta-joke
Meta-joke refers to several somewhat different, but related categories: self-referential jokes, jokes about jokes (also known as metahumor), and joke templates.
 
Self-referential jokes
This kind of meta-joke is a joke in which a familiar class of jokes is part of the joke. Examples of meta-jokes:
(...)
. A dyslexic man walks into a bra.
 
Google Books
Notes on a Beermat:
Drinking and Why It’s Necessary
By Nicholas Pashley
Toronto, ON: Polar Bear Press
2001
Pg. 195:
So this dyslexic walks into a bra.
 
MetaFilter
A dyslexic walks into a bra.
posted by transient at 9:35 AM on December 20, 2001
 
Google Groups: rec.humor.jewish
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Andi Stephens
10/13/02
(...)
Dyslexic man walks into a bra….
 
Google Groups: alt.wisdom
A few Groaners
Linda
8/5/04
(...)
5. A dyslexic man walks into a bra.
 
Google News Archive
2 February 2006, Defuniak Springs (FL) Herald, “Points to ponder” by Ron Kelley, pg. 4A, col. 1:
A dyslexic man walks into a bra…
   
Google Groups: rec.boats
OT: Top 50 Jokes of All Time
Wayne. B
10/26/10
(...)
3.  ‘‘Dyslexic man walks into a bra’‘
 
OCLC WorldCat record
A dyslexic walks into a bra : a compendium of the best jokes, gags and one-liners
Author: Nick Harris
Publisher: London : Michael O’Mara, 2011.
Edition/Format:   Book : Humor, satire, etc. : English
Database: WorldCat
Summary:
It’s the classic gags that keep people laughing time after time, and Nick Harris has collected together a bumper batch of the best jokes that are guaranteed to have anyone rolling in the aisles.
   
Google Groups: alt.usage.english
The Legendary Bar Jokes Thread
Anton Shepelev
12/1/11
(...)
(8)  [James Hogg]  A metathesis walks into a bra
(...)
67) [Reinhold {Rey} Aman]  A dyslexic walks into a rab.