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1.
A term used in forums to mean an unexperienced and enthusiastic weapon(usually a firearm)owner who pretends to be a seasoned operator. The phrase came about as a result of an over the top character in a famous satirical thread.
I am a part time mall ninja and I am currently recieving the escalator assualt training.B-)
by xd-40 February 27, 2005
 
2.
A term used in the firearm community to describe an individual who is obsessed with tactical, paramilitary style firearms and modifications, particularly firearms composed mostly of plastic. Such individuals are usually un-experienced novices who compulsively overpay for weapons and accessories not worth their weight in dog crap because such items looked cool in movies and video games.
Jeff: "Dude check out my new AR-15. Its got quad rails, a flashlight/ laser combination, a dummy grenade launcher, a bayonet, a telescoping stock, and an ACOG scope!"

Matt: "Dude check out my .30/06 Remington 700 with a custom walnut stock and a Leupold scope. I can kill a deer at 500 yards with factory ammo! Can your AR do that?"

Jeff: "Uh, No..."

Matt: "Didn't think so. Admit it. You're a damn MALL NINJA!"
by Piecemaker June 22, 2010
 
3.
A person, usually high school to college aged young white or Asian male, who purchases weapons, such as samurai swords, maces, spears, scimitars, fancy looking knives, daggers, and nun-chucks at a shopping mall, usually from stores like Merlot's Cutlery, China Capital Arts, or various privately owned Oriental gift shops. Will talk trash to each other about the quality of their swords, which they will never use for anything in real life. Some of these people will pay high prices to purchase "better" swords on the internet, in the range of $300 to several thousand dollars, to out-do their friends or enemies who bought their blades at the local shopping mall. These people are often goths, thugs, or kids who are at the bottom of the social totem poll.
Dude, Mike owns like 10 samurai swords, 4 pairs of nunchucks, a bowstaff, and throwing stars. He got them all at China Capital Arts. He is such a mall ninja.
by Lupara2012 July 28, 2012
 
4.
A young male who wears a dark trench coat and obsesses with death, violence, violent video games, and firearms (in a way vastly different from firearms collectors and those who enjoy shooting). This type of young male may have long messy hair. He also resembles the spazzy, violent, and unpredictable criminals that perpetrated the Trolley Square (Utah) and Von Maur (Omaha Nebraska) mall shootings. This type of male is barely interested in females, and may have recently been dumped.

The term "ninja" seems to have stuck to these types of young males because they behave as if they are invincible. Plus, the weapon of choice in these mall shootings has been a long weapon (rifle), which the mall ninja seems to prefer because it's length makes them feel they are wielding a sword (like a ninja).
"I'm worried about Jason, he always wears a trench coat, he plays violent video games, is obsessed with firearms and death. You know, since Jennifer dumped him, he's becoming a mall ninja."
by repeal17thamendment January 11, 2010
 
5.
A stupid nickname that kids in Pa/Nj/De area came up with for themselves if they are actually mall rats. Then they had to incorporate the whole Ninja/Pirate war thing... Also see Mall Pirate
See those kids at hot topic? They call themselves Mall Ninjas.
by toee February 10, 2006