A classic programming joke is:
 
Q: How did the programmer die in the shower?
A: By following the instructions on the shampoo bottle: “Lather. Rinse. Repeat.”
 
The programming joke was posted on the newsgroup rec.humor on October 2, 1990. The joke has been printed on several images.
     
 
Google Groups: rec.humor
Funny acronyms request
Julia Wilkinson
10/2/90
(...)
Did you hear of the programmer who died in the shower? He had a bottle of shampoo which read: Lather. Rinse. Repeat. 
 
Google Groups: news.admin
UUPSI’s new rules
Peter da Silva
3/19/91
(...)
Only if you choose to read the letter like a computer program. Hey, did you hear about the computer programmer who died in the shower? The instructions read “lather, rinse, repeat”... and he died of a stack overflow.
 
Google Groups: rec.humor
Programmer joke(hopefully) 😊
Drac/Natas
1/4/92
How did the Computer Programmer die in the shower ??
He followed the instructions on the shampoo bottle -
                         
LATHER, RINSE, REPEAT
   
Google Books
Debugging Strategies For .NET Developers
By Darin Dillon
Berkeley, CA: Apress
2003
Pg. 59:
Q: How do you keep a computer programmer in the shower forever?
A: Give him a bottle of shampoo with the directions, “Lather, rinse, repeat.”
 
Google Books
An Introduction to Programming with Java Applets
By Elizabeth S. Boese
Sudbury, MA: Jones and Bartlett Publishers
2010
Pg. 201:
Why did the programmer get stuck in the shower?
Because the shampoo bottle said, “Lather, Rinse, Repeat.”
 
Reddit—ProgrammerHumor
You all have probably already seen these, but here’s a compilation of some programmer jokes I found. (self.ProgrammerHumor)
submitted October 21, 2012 by alphaorionis
Q. How did the programmer die in the shower?
A. He read the shampoo bottle instructions: Lather. Rinse. Repeat.
(meta-joke: Eventually the bottle would be empty and an exception would be raised.)
 
Google Books
The Handbook of Contemporary Semantic Theory
By Shalom Lappin and Chris Fox
Malden, MA: John Wiley & Sons, Inc.
2015
Pg. 455:
Recall the old joke of the computer programmer who died in the shower? He was just following the instructions on the shampoo bottle: “Lather, rinse, repeat.”
   
Reddit—Jokes
A programmer was found dead in the shower this morning ...
submitted October 27, 2015 by Bokbreath
Next to him was found a shampoo bottle marked ‘Lather, Rinse, Repeat’.
 
Reddit—Jokes
Why did the computer programmer get stuck in the shower forever?
submitted October 29, 2015 by YourNameIsIrrelevant
Because the instructions on the shampoo bottle said to “1. Lather 2. Rinse 3. Repeat”
 
DevDojo
10 Awesome Programming Jokes
by devdojo
on January 2, 2016
(...)
Q: How did the programmer die in the shower?
A: He read the shampoo bottle instructions: Lather. Rinse. Repeat.