Originating from several 2000-2001 discussions at internet forums devoted to firearms, in which a poster bragged about his firearm expertise while claiming to be a "Sergeant of a three-man Rapid Tactical Force" at an American mall, trained in "ninjitsu." He was soon nicknamed "the mall ninja."[1]
(derogatory,informal) A person who claims to be an expert on weaponry, often to the point of disdaining popular weapons and preferring expensive and exotic ones along with equally expensive accessories, and likes to brag about their supposed expertise, but often exposes their ignorance in discussions, sometimes making improbable claims about their experience or weapon use.
2002 September 13, "Rawhide Clyde", “Re: Are Striders worth their price?”, in rec.knives[1] (Usenet):
I own a Strider [knife]. Nope, I'm not a mall ninja or secret squirrel but it gives me pleasure to own them.
2005 April 30, Mike Kelly, “Re: I got to stay out of the politic groups...”, in talk.politics.guns[2] (Usenet):
I too abandoned those groups. Granted, I was one who had my mind made up for the most part, but not entirely. I just grew frustrated with the kindergarten sophistry, mall ninja bravado, and so on.
2007, Patrick Sweeney, The Gun Digest Book of the AR-15, Volume 2[3], Gun Digest Books, →ISBN, page 219:
No big deal, unless you're anal about being mil-spec "correct" to impress your mall ninja buddies.
2008 March 6, "WuzYoungOnceToo", “Re: Hey pickle! try again”, in rec.gambling.poker[4] (Usenet):
You know...like the delusion that you were ever a LEO [law enforcement officer], while you sound far more like a frustrated mall ninja.
2016, Bryce M. Towsley, Prepper Guns[5], Skyhorse Publishing, →ISBN:
A compound bow is much better [than a crossbow] in every respect, expect maybe for exciting those mall ninjas who, when they are not watching The Walking Dead, hide in their mom's basement and fantasize about Lara Croft.