A drunken driver pinched by Upper West Side cops blabbed about all the weapons he had back in his apartment — and officers who searched it found a mother lode, authorities said Monday.

Carlos Costas, 34, showed signs of being under the influence when cops stopped him for driving his red 1996 Honda minivan erratically at around 1 p.m. Saturday at the intersection of Columbus Avenue and West 87th Street near his home, officials said.

Authorities said they found two bottles of booze between the driver’s and front-passenger seats and arrested Costas.

While in custody, Costas began talking about having illegal guns and said he had been fighting with his 33-year-old girlfriend, whom he lives with in a third-floor apartment at 59 W. 87th St., police said.

Officers conducted a wellness check at the address, where a search warrant was executed.

Inside the residence, police allegedly found the horde of weapons, which included a defaced, .38-caliber Rossi revolver, a Muscle Man stun gun, two long-range Airsoft firearms, a BB gun, more than 150 rounds of ammunition and more than a dozen knives.

A photo that the NYPD tweeted of the weapons also showed a whip and two sets of handcuffs.

Police found a bag of purported cocaine on Costa’s girlfriend, Tasha Cruz, cops said. Two zip bags of marijuana were also found in the apartment, they said.

Costas told cops that all of the weapons belong to him, but authorities charged both him and Cruz with 21 counts of criminal possession of a weapon.

He was also hit with charges of operating a car while intoxicated, aggravated unlicensed operator and operating a motor vehicle without an inspection, police said. He was given a violation for driving without a license, too.

Cruz was also charged with criminal possession of a controlled substance.

At their arraignments in Manhattan Criminal Court, Costas was ordered held in lieu of $5,000 bail, while Cruz was released on her own recognizance.

“I’m totally surprised,” said a neighbor. “They live right above me, and I never hear anything.”

The neighbor called Costas “a nice guy,” adding, “I can’t say anything negative about him. He is very helpful, helps pick up my shopping bags. He always holds a parking spot for me.”

Costas was also busted on July 6 for drunken driving. A month later, he was arrested for criminal possession of a controlled substance and aggravated unlicensed operator. Cruz has one prior sealed arrest.

Additional reporting by Elizabeth Rosner