Gallery openings tend to be staid affairs. White wine, art-world hobnobbing and maybe dinner.

O’Flaherty’s, a scrappy gallery in the East Village of Manhattan that’s named after a nonexistent Irish pub, sought to invert the whole notion of the summer group show. First, it held an “open call” in which anyone — starving artists, children, even Terrence Koh, an established artist — could submit their work and see it hung in a New York City gallery. (More than a thousand people dropped off submissions, the gallery said.)

Then O’Flaherty’s invited them all, and their Instagram followers, to a big opening last Thursday night. It was a well-planned recipe for mayhem.

Ten minutes before the 8 p.m. opening, Jamian Juliano-Villani, an artist who founded the gallery with her longtime friend Billy Grant, 37, was buzzing around the ramshackle storefront gallery, putting out last-minute fires and chugging from a bottle of Evan Williams bourbon.

“This is disgusting,” said Ms. Juliano-Villani, 35, referring to the work being shown. She wore a bright red tank top with a fluorescent green miniskirt, a cigarette dangling from her lips. Then she turned off all the lights and started letting people in.

As visitors streamed through the front door, each was handed a small flashlight and the pitch-black gallery was soon illuminated by a swarm of LED beams. What the attendees saw was a maniacal mishmash of art: more than 1,100 works covered every square inch of the cramped gallery.

There were oil paintings of genitalia, a still-life of peaches, a shovel twisted like a pretzel, a silk-screen of someone who looks like Al Pacino, a wall clock with mismatched numbers, a pair of panda prints by Rob Pruitt, a box of disposable gloves, a black dildo, a signed photograph of Justin Bieber as a child, a patterned swastika with a happy face. Cans of Budweiser and Coors were served in a plastic tub.

Many of the early arrivals were artists looking for their work. “I’m pretty proud of it,” said Matt Held, an art handler in his 50s who came with his 14-year-old daughter. He found his oil painting — a portrait of a friend in a pink shirt — hanging in the hallway.

Michael Crinot, a 20-year-old student, found his work in the office. “I made it,” he said, admiring a portrait of his severed head painted on a Cheez-It cracker box. “That moment exists.”

The bathroom was plastered in art as well, including a toilet seat with red lipstick marks by Dan Colen. In a side room, whenever guests entered, a motion detector would set off loud power tools hidden under the floorboards, causing some viewers to scream.

“You thought you couldn’t be in a more disrespectful group show and you were wrong,” the gallery founders wrote in a statement. They took any piece anyone brought in, the statement said, “whether it was awesome or total trash, and tried to make it an idea.”

By 8:30 the gallery was mobbed. The atmosphere was somewhere between a haunted house and a sex club. In a span of a few seconds, you could bump into an artist crouched over to find their work, get blinded by a flashlight, have beer spilled on you, and see a young man knock over a painting while taking a photo of his friend, posing with a watercolor hung behind a garbage can.

Few wore masks, and the words “superspreader” and “monkeypox” could be heard in the airless gallery.

Outside, hundreds lined up along Avenue C, past a community garden, and down the block along East Fourth Street. Hundreds more amassed in front of the gallery, turning the opening into an impromptu block party.

There were young artists in torn tank tops and carrying tote bags. Older East Village types with ponytails and walking sticks. Performance artists who turned the sidewalk into their stage and gallery — a Salon de Refusés on top of a Salon de Refusés. There were also a handful of familiar art-world fixtures including the artists Rachel Rossin and Richard Phillips, and the gallery owners Alexander Shulani and Max Levai.

The block party felt like a throwback to a New York of a different era, when Deitch Projects and other galleries tapped into a frenzied downtown art scene and held carnivalesque openings that spilled onto the sidewalk and blurred the lines of art, music, fashion and nightlife.

O’Flaherty’s may have done that too well. At 8:50 p.m., the police arrived. Ms. Julio Vallani went outside to discuss the situation. This was an art opening, she explained. People came to see their work on display and to support their friends.

The police took a look inside and did not like what they saw. One officer, speaking on the phone to his precinct, estimated that there were 3,000 people outside the gallery. “Clear it out, or I’m going to shut it down right now,” Timur S. Popal of the Ninth Precinct told the gallery owners. “This is unsafe.”

Ms. Julio-Vallani surveyed the circus atmosphere and seemed to grasp the situation at hand. She stormed back inside the gallery, yelling, “Out! Out! Out!!! Everyone out!”

Guests trickled out and rejoined the block party, which now included several squad cars and more police officers trying to disperse the crowd. “There’s no more art, go home,” one officer said.

By 10 p.m., there were still a few dozen stragglers outside, some of whom banged on the storefront windows, hoping the gallery would reopen. Ms. Juliano-Villani, who at this point had finished the whiskey and moved to a bottle of tequila, couldn’t believe their determination.

“And this stuff sucks, too,” she said, gesturing to the art on the office walls.

She went outside and rolled down the security gate, to reinforce the message that the gallery was closed for the night. While several officers roamed the gallery, Ms. Juliano-Villani and her staff spread the word that there would be an after-party at Nublu, a dance club a few blocks north.

“Only eight things got damaged,” Ms. Juliano-Villani said on her way out.