Mr Jon Lewis Alexander, 54, had spent 30 years in the military, had been a prison guard and a private investigator and had once helped extradite federal prisoners.
So he was unimpressed when a man walked into a liquor store in southwest Missouri where he worked, pulled out a handgun and demanded money.
The store's video shows Mr Alexander calmly pushing the gun aside and drawing his Walther PPX 9mm handgun, pointing it at the would-be robber's mouth.
The robber then backs away and runs out of the store. No shots were fired and no one was injured in the incident late last week, AP reported.
The police are still looking for the would-be robber. "One of the policemen told me later, 'You're a lucky man'," Mr Alexander told the Springfield News-Leader. "I said, 'I think he (the robber) is a little luckier than I am'."
He said the man had walked in smoking a cigarette, which he was promptly told to put out.
The man then reached for his gun and demanded "all the (expletive deleted) money," News-Leader.com reported.
The veteran reacted quickly, pushing down the robber's gun-bearing right arm.
Mr Alexander then drew his own weapon with his right hand and, according to the report, threatened to "blow his (expletive deleted) head off".