What a pee-brain!

A retired NYPD cop lost her handgun during a bathroom break in Midtown, The Post has learned.

Kim Sciarrino, 48, was visiting the Urbanspace@Vanderbilt food hall when nature called, law enforcement sources said Thursday.

Sciarrino ducked into the women’s room to take care of business but accidentally left her .380-caliber Ruger LCP pistol on a shelf above the toilet when she finished up and left, sources said.

Upon realizing what she’d done, Sciarrino went back to get the gun but found it was gone around 12:15 p.m. Wednesday, sources said.

The Suffolk County resident told cops she didn’t see anyone reach in and grab the seven-shot, semiautomatic pistol while she was inside the stall, and there’s no surveillance video to identify the thief who swiped it, sources said.

Diners and workers at the upscale food court near Grand Central Terminal were outraged at the ex-cop’s carelessness.

Ronaldo Sanchez, 52, who was eating lunch from the Red Hook Lobster Pound, said, “I am a carpenter and always carry my hammer on the side, and sure enough if I go to the bathroom I’ll take the hammer off — but I can’t leave without the hammer, it’s my livelihood.”

“Thank God no one got hurt,” he said.

“Imagine if someone came out of the bathroom yesterday and emptied the clip.”

Health care worker Greg Wong, 50, asked, “Why is she carrying a gun if she is a retired cop?”

“I’m glad she isn’t on active duty,” he added.

A worker at the Two Tablespoons vegetarian eatery recognized Sciarrino from her Facebook page and said that when cops came to investigate Wednesday’s incident, “she didn’t seem upset, to be honest.”

“She was too calm, like way too calm,” Stephanie Morales said.

“Most everyone has been gossiping about it. What an idiot!”

NYPD cops who get what’s known as a “good-guy letter” when they retire are eligible for concealed-carry pistol permits valid throughout the state and New York City.

But failure to “properly safeguard” a firearm is grounds for suspension and/or revocation of a permit, according to a handbook issued by the Suffolk County Police Department.

Sciarrino is married to a fellow retired NYPD cop, Maverick Sciarrino, who refused to discuss his wife’s blunder.

“It’s a private matter. Get off my property,” he told The Post at their home in West Babylon, LI.

The NYPD said it was “investigating the loss of the firearm.” The Suffolk County PD didn’t return requests for comment.

The Ruger LCP is a compact, American-made handgun that has a 2-3/4-inch barrel and weighs just 9.6 ounces.

It’s marketed as the “perfect choice” for a backup weapon for law enforcement officers or for concealed-carry by civilians.

In February 2010, then-Texas Gov. Rick Perry — now President Trump’s energy secretary — famously used a model with a built-in laser sight to blast a coyote that menaced his puppy while they were out for a run near Austin.

To commemorate that one-shot kill, Ruger released a limited-edition “Coyote Special” with etchings that included a Texas “Lone Star” and a coyote howling at the moon.