“If you can’t dazzle them with brilliance, baffle them with bullshit” is a jocular saying that has been cited in print since at least 1972. “If you can’t dazzle them with brilliance, riddle them with bullets” is a jocular anti-proverb.
 
“If you can’t dazzle them with brilliance, riddle them with bullets” has been cited in print since at least April 1999 and has bee printed on bumper stickers. A Twitter message in 2012 claims this as an “old Texas saying,” but there’s no evidence that points to a specific place of origin for the saying.
 
   
Google Groups: alt.games.mechwarrior2
SPECTRE  
4/18/99
(...)
IF YOU CAN’T DAZZLE THEM WITH BRILLIANCE,
RIDDLE THEM WITH BULLETS.
 
Google Groups: alt.games.mechwarrior2
SPECTRE  
4/27/99
(...)
IF YOU CAN’T DAZZLE THEM WITH BRILLIANCE,
RIDDLE THEM WITH BULLETS.
 
Google Books

A Smorgasbord of E-Mail and Internet Wit Blended with Humorous Incidents from the Author’s Wild and Wooly Life
By Marv Rubinstein
Rockville, MD: Schreiber Pub.
2000
Pg. 108:
IF YOU CAN’T DAZZLE THEM WITH BRILLIANCE RIDDLE THEM WITH BULLETS
   
Google Books
Yada, yada, yada.com.org.edu.gov.email:
What I learned on the WWW/Internet
Joan E. Miller
San Jose, CA: Writers Club Press
2000
Pg. 19: 
If you can’t dazzle them with brilliance, riddle them with bullets.
 
Google Books
Laugh Out Loud:
A Selection of the Finest Internet Humour, Anecdotes and Wisdom
By Vivienne Smithdorf and Vanessa Wilson
Sandton, South Africa: Vsquared
2004
Pg. 170:
If you can’t dazzle them with brilliance, riddle them with bullets.
 
Twitter
Dat_boi P‏
@lukitzpaul  
Old Texas saying, “If you can’t dazzle them
with your manliness, riddle them with bullets. #teamfollowback
10:29 PM - 23 Feb 12