The 73-year-old had reportedly had an argument on Saturday with customers at the bar in the town of Cilavegna, Pavia, over the queue to the slot machines, La Repubblica reported on Monday.
Apparently unable to resolve the dispute, the pensioner turned up at the bar the following day with a lust for vengeance and a Smith & Wesson 357 magnum gun, a knuckle-duster and a flick-knife.
Police were called to the scene where they arrested the man, who has a clean record. No injuries were reported.
But, as police discovered, the shotgun was just the tip of the iceberg. When they inspected the man's home they uncovered an "arsenal" of weapons.
The pensioner's collection included a Stahl shotgun, a Franchi Para rifle, a Beretta semi-automatic shotgun, a silencer and around a hundred bullets.
Two more guns found at the man's home, including a Beretta shotgun and a Breda rifle, had been registered.
Police also found two bayonets, a sabre, two machetes and even a samurai sword. The weapons have now been seized.
They also found four metal plates, two belonging to the Carabinieri, one from the fire department and another to the police.
In March The Local reported that a woman, believed to be in her seventies, robbed a bank near Florence with a toy gun.