A dirty joke definition of a “Texan” is “a Mexican ("wetback") who couldn’t swim to Oklahoma.” The “joke” was popular in Oklahoma, but not in Texas.


Google Books
Semi-Tough
by Dan Jenkins
Thunder’s Mouth Press
2006
original printing—New York: Atheneum, 1972
Pg. 11
“Say, Puddin. You know what a Texan is?”

Puddin half-turned around.

He laughed and said to the room, “Cat done told me it was a Mexican on his way to Oklahoma.”

Google Books
The Dirty Joke Book
by Mr. “K”
Citadel Press
2001
Pg. 90:
WHAT’s the definition of a Texan?
A Mexican on his way to Oklahoma.

canonical list of funny definitions
Texan - a Mexican that couldn’t swim all the way to Oklahoma

YAHOO! Answers (since removed)
What do you call a Mexican that runs out of money on his way to Oklahoma?
a Texan

Google Groups: rec.humor
Newsgroups: rec.humor
From:
Date: 30 Jul 91 00:01:36 GMT
Local: Mon, Jul 29 1991 8:01 pm
Subject: Re: W. Va. Jokes, Re: Texans

Do you know what a Texan is?
A Mexican on his way to Oklahoma.

American Dialect Society listserv
Date:  Fri, 22 Apr 2005 18:11:34 -0400
From:  Wilson Gray
Subject:  “Wag” = “carry”
(...)
Also FWIW, Dr. Phil, like Bill Moyers, was born in Oklahoma but reared in Texas. Old joke:

Q. What’s a Texan?
A. A Mexican on his way to Oklahoma.