Dr Pepper is a carbonated soft drink that was created in the 1880s by Charles Alderton in Waco, Texas. A popular off-color Dr Pepper joke is:
 
Q: Why does Cr Pepper come in a bottle?
A: Because his wife died.
 
The joke has been cited in print since at least the 1970s and made several joke books in the 1980s. A second joke was posted to the newsgroup alt.tasteless.jokes on July 2, 2001:
   
Q: Why does Dr Pepper come in a can?
A: His bottle is full.
   
   
Wikipedia: Dr Pepper
Dr Pepper is a carbonated soft drink marketed as having a unique flavor. The drink was created in the 1880s by Charles Alderton in Waco, Texas and first served around 1885. Dr Pepper was first nationally marketed in the United States in 1904, and is now also sold in Europe, Asia, Canada, Mexico, Australia, and South America, as well as New Zealand and South Africa as an imported good. Variants include a version without high fructose corn syrup, Diet Dr Pepper, as well as a line of additional flavors, first introduced in the 2000s.
 
Google Books
Truly Tasteless Jokes
By Blanche Knott
New York, NY: Ballantine Books
1982
Pg. 107:
Why does Dr. Pepper come in a bottle?
Because his wife died.
     
Google Books
National Lampoon
Volume 2, Issues 42-53
1982
Pg. 14:
Q: Why does Dr. Pepper come in bottles?
A: Because his wife died.
 
Google Books
Rednecks
By Larry Wilde
New York, NY: Bantam Books
1984
Pg. 63:
Why does Dr. Pepper come in a bottle?
Because his wife died.
 
Google Groups: net.jokes
Dr. Pepper
s. dugan
8/8/85
Here’s an oldy but a goodie.
 
Question:  Why does Dr. Pepper come in a bottle?
Answer:  Because his wife died.
(Oh, how gross!)
 
Google Groups: rec.humor
Dr Pepper
Matthew R Palmer
10/21/95
Why does Dr Pepper come in a bottle?
His wife died
 
Google Groups: alt.tasteless.jokes
Dr. pepper joke
(...)
Jeremy Rae
6/30/96
.(JavaScript must be enabled to view this email address) wrote:
> Q:  why does Dr. Pepper come in a bottle?
> A:  because his wife died!
 
Or:
Q:  Why does Dr. Pepper come in a can?
A:  Becuase his wife was on the rag!!!
   
Google Groups: alt.tasteless.jokes
Why does Dr. Pepper come in a bottle?
G - P
7/2/01
Cause his wife died!
 
G S
7/2/01
Why does Dr. Pepper come in a can?
His bottle is full
 
Twitter
JoshJoshJones
‏@JoshJoshJones
why does Dr Pepper come in a bottle? Because his wife’s dead.
6:15 AM - 1 Dec 2008
 
Google Books
Jokes for Blokes:
The Ultimate Book of Jokes Not Suitable for Mixed Company
By Llewellyn Dowd and Phil McCracken
London: Ebury Press
2011
Pg. 361:
Why does Dr Pepper come in a bottle? Because his wife died.
   
Reddit
Why does Dr. Pepper come in bottles?
submitted August 30, 2016 by Yngvar_Stormblade
His wife is dead.
 
Reddit
Why does Dr Pepper come in a can?
submitted October 2, 2016 by TheBongoMan
Because his wife left him.