“Never ruin an apology with an excuse” is a popular saying of uncertain authorship. “Quote for the time being:  Never ruin an apology with an excuse” was cited in September 1996 and “Just remember the old saying: ‘never ruin an apology with an excuse’” was cited in October 1996. In April 1997, the saying was credited to Kimberly Johnson.
 
“Never mess up an apology with an excuse” was cited in 1998. The saying has been printed on many images, often incorrectly credited to Benjamin Franklin (1706-1790).
   
 
Google Groups: rec.autos.misc
Shifting Problems: 85 Accord Automatic Transmission
Denver Sommers
9/27/96
(...)
email from:                               
Denver and Rose Sommers
.(JavaScript must be enabled to view this email address)
Leola, Pennsylvania
 
Quote for the time being:  Never ruin an apology with an excuse.
   
Google Groups: rec.autos.driving
hesitation with 89 Corolla SR5
Denver Sommers
10/1/96
(..)
email from:                               
Denver and Rose Sommers
.(JavaScript must be enabled to view this email address)
Leola, Pennsylvania
 
Quote for the time being:  Never ruin an apology with an excuse.
 
Google Groups: misc.kids.pregnancy
Feeling INSANE!!!
David Innes
10/30/96
(...)
So congratulations!  You’ve got a good excuse for your terrible mood. Just remember the old saying: “never ruin an apology with an excuse.”
 
Google Groups: alt.humor
“Never” Quotes
Keith E. Sullivan
4/22/97
(...)
Never ruin an apology with an excuse. —Kimberly Johnson
   
Google News Archive
20 December 1997, The Weekend Daily News (Pullman, WA & Moscow, ID), Ann Landers (syndicated advice column), pg. 6B, col. 2:
Gem of the Day (Credit Kimberly Johnson): Never ruin an apology with an excuse.
   
Google Books
Mademoiselle: The Magazine for the Smart Young Woman
Volume 104
1998
Pg. 64 ad:
Never mess up an apology with an excuse.
   
Google Groups: alt.support.tall
98-99 Dodge Intrepid is a pretty good fit.
Heather
5/18/99
(...)
“Never mess up an apology with an excuse”
 
Google Groups: alt.support.stop-smoking
Thoughts for the daze
Marcie M
2/23/00
(...)
13. Never mess up an apology with an excuse.
     
Google Books
The Sweetest Thing
By Jill Shalvis
New York, NY: Forever
2011
Pg. ?:
“Never mess up an apology with an excuse.”
CHLOE TRAEGER
 
Google Books
$500,000 Worth of Inspiring Quotations for Our Times
By Web Augustine
Zinfandel Publishing
2911
Pg. 37:
“Never mess up an apology with an excuse.”
Unknown
 
Google Books
Restored Lives:
Recovery from divorce and separation
By Erik Castenskiold
Oxford: Monarch Books
2013
Pg. 126:
Benjamin Franklin said, “Never ruin an apology with an excuse.”