“The main reason Santa is so jolly is because he knows where all the bad girls live” is a Christmas joke that has been printed on many images. Authorship is uncertain.
   
“The main reason Santa is so jolly is because he knows where all the naughty girls live” was posted to the newsgroup comp.sys.acorn.apps on February 18, 1998. “The main reason Santa is so jolly is because he knows where all the bad girls live” was posted to the newsgroup alt.tasteless.jokes on May 20, 1998. No author was credited.
 
“Santa is very jolly because he knows where all the bad girls live” was posted to the newsgroup alt.jokes on March 5, 1999 and credited to American stand-up comedian and commentator Dennis Miller.
   
“The main reason Santa is so jolly is because he knows where all the bad girls live” was posted to the newsgroup uwo.comp.helpdesk on April 2, 1999 and credited to New York-born stand-up comedian George Carlin (1937-2008). The website GeorgeCarlin.com stated in 2004 that the joke does not come from George Carlin.
     
 
Google Groups: comp.sys.acorn.apps
JunkMail Rules
Luke Bosman
2/18/98
(...)
* The main reason Santa is so jolly is because he knows where all the naughty girls live.
     
Google Groups: alt.tasteless.jokes
Words to Live By (X version)
Sinnful
5/20/98  
(...)
Dear Santa, all I want is your list of naughty girls.
(...)
The main reason Santa is so jolly is because he knows where all the bad girls live.
   
Google Groups: alt.flame.macintosh
BIG reasons why the Mac OS is better than Windows
Charles Davis
12/31/98
(...)
“The main reason Santa is so jolly is because he knows where all the bad girls live.”
 
Google Groups: alt.jokes
Dennis Miller’s rants
Kevin Ridolfi
3/5/99
Dennis Miller:
Don’t sweat the petty things and Don’t pet the sweaty things.
One tequila, two tequila, three tequila, floor.
If man evolved from apes why do we still have apes?
Santa is very jolly because he knows where all the bad girls live.
 
Google Groups: uwo.comp.helpdesk
Friday Humor
Jera Anderson
4/2/99
My first contribution to Friday’s Humor may be recycled, but then, what isn’t.  As I often tell my band’s audience, “Hey, that last song may not be one of your favorites, but it’s got a lot of the same notes!”
George Carlin’s Wit

1) Don’t sweat the petty things and don’t pet the sweaty things.
2) One tequila, two tequila, three tequila, floor
3) Atheism is a nonprophet organization.
4) If man evolved from monkeys and apes, why do we still have monkeys and apes?
5) The main reason Santa is so jolly is because he knows where all the bad girls live.
 
21 June 1999, The Beacon Journal (Akron, OH), “Pearls of Wisdom,” pg. B1, col. 1:
The main reason Santa is so jolly is because he knows where all the bad girls live.
 
Google Groups: alt.penpals.forty-plus-yrs
JOKE: George Carlin One Liners (clean)
Isle of Skye
5/15/99
George Carlin Witticisms
1)  Don’t sweat the petty things and don’t pet the sweaty things.
2)  One tequila, two tequila, three tequila, floor.
3)  Atheism is a nonprophet organization.
4)  If man evolved from monkeys and apes, why do we still have monkeys and apes?
5)  The main reason Santa is so jolly is because he knows where all the bad girls live.
 
Google Groups: alt.support.loneliness
JOKE CENTRAL—George Carlin’s Simple Truths
Barbara
6/24/99
Some simple truths of life by George Carlin…
1. Don’t sweat the petty things and don’t pet the sweaty things.
2. One tequila, two tequila, three tequila, floor.
3. Atheism is a non-prophet organization.
4. If man evolved from monkeys and apes, why do we still have monkeys and apes?
5. The main reason Santa is so jolly is because he knows where all the bad girls live.
 
29 October 1999, Florida Today (Melbourne, FL), “Another Good Tale Goes Up in Flames” by Milt Salamon, pg. 12A, col. 4:
- “WEIRD STUFF” is what one e-mail forwarder (maybe it was Don Boyer) labeled a great collection of sayings. They’re subtitled “Philosophy of Life Per George Carlin.” Here goes:
 
1. “One tequila, two tequila, three tequila, floor.”
2. “Atheism is a non-prophet organization.”
3. “If man evolved from monkeys and apes, why do we still have monkeys and apes?”
4. “The main reason Santa is so jolly is because he knows where all the bad girls live.”
 
GeorgeCarlin.com (October 18, 2004)
THIS IS NOT GEORGE CARLIN:
Philosophy of George Carlin
1. Don’t sweat the petty things and don’t pet the sweaty things.
2. One tequila, two tequila, three tequila, floor.
3. Atheism is a non-prophet organization.
4. If man evolved from monkeys and apes, why do we still have monkeys and apes?
5. The main reason Santa is so jolly is because he knows where all the bad girls live.
 
Google Books
It’s a Man’s World:
800 Jokes from the Guy’s (Warped) Point of View
By Judy Brown
New York, NY: Barnes & Noble Books
2005
Pg. 40:
Santa is very jolly because he knows where all the bad girls live. — Dennis Miller
   
Google Books
Release Your Inner Old Fart
By Mark Leigh
London: Michael O’Mara Books
Pg. ?:
‘Santa is very jolly because he knows where all the bad girls live.’
DENNIS MILLER
 
Google Books
Fat Poo’s Christmas Jokes
By Peter Crumpton
PeteyRF Creative
2015
Pg. ?:
The main reason Santa is so jolly is because he knows where all the bad girls live