On Oct. 3, 1992, singer Sinéad O’Connor created a scandal when, at the end of a performance on “Saturday Night Live,” she produced a photo of Pope John Paul II and proceeded to rip it into 10 tiny pieces.

“Fight the real enemy!” she commanded, as the crowd in Rockefeller Center’s Studio 8H looked on in stunned silence — the first time a musical guest didn’t draw applause.

Backstage, “SNL” honcho Lorne Michaels was nonchalant. He turned to cast member David Spade, shrugged, and said, “Irish.”

During the next commercial break, Spade walked onto the stage and grabbed one of the torn photo pieces.

“This will be a nice memento if anyone ever remembers it happening,” Spade recalls thinking in his new memoir, “Almost Interesting,” out Tuesday.

The next day, while doing laundry at his Upper West Side apartment, the comedian saw a report on “Inside Edition” about the O’Connor incident. The news program had the actual photo, which had been taped together minus a single piece — Spade’s.

On Monday, Spade was hauled into a producer’s office and confronted by NBC security, demanding he return the piece of the photo. As it turned out, a crew member had collected the other pieces and sold them to “Inside Edition” for $10,000, and security believed Spade might be in on it. Spade gave his piece back.

“I regret that. No one cared, but security had to make a point,” Spade tells The Post. He sarcastically adds, “They were cracking a case.”

One memento from his “SNL” days Spade still has is a tattoo given to him by Sean Penn for a 1995 segment.

“I didn’t really want to get a tattoo,” Spade says. “I was just out of ideas.”

The comedian had heard at a party that Penn was learning body inking by practicing on potatoes and pig ears, so he got the actor’s number from cast mate Jon Lovitz and asked for a tattoo.

Spade chose a design, but Penn wasn’t skilled enough for something so complicated. Instead, the two settled on Calvin from “Calvin and Hobbes.”

“I’ve never been happy with it,” Spade says. “I showed it to [Penn’s ex-fiancée] Charlize [Theron] once. She asked, ‘Is that a real story?’ Once she saw my pasty little arm, she said, ‘Yeah, I’ll just take your word for it next time.’ ”

‘Almost Interesting” is a dishy, anecdote-driven look at Spade’s life, from his childhood to his seven years on “SNL” and beyond.

“There were a few stories that were sort of tent-pole-ish,” he says. “I wrote those, and [the editors] were like, ‘You’re a fourth done.’ So then I just made it about my life.”

Spade, 51, grew up “the shortest and poorest” in Scottsdale, Ariz. His father had “scrammed on the family” early on, and Spade’s mother eventually remarried. When Spade was 15, his stepfather committed suicide.

“That stuff affects you in different ways, so I don’t really know where the damage is,” Spade says. “You can ask girls that date me that have a list of [my] problems they always want to show me. I’m sure that’s on there.” (The never-married comedian has dated Lara Flynn Boyle and Heather Locklear and has a 7-year-old daughter, Harper, born with model ex Jillian Grace.)

He got into stand-up comedy as a teen, playing local clubs to a middling reception. The turning point came when Spade was attending Arizona State University and entered a talent show. He killed with jokes such as, “I got a new car. It’s not really new. It’s an old UPS truck. I got it so I can park wherever I want.”

As the actor recalls now, “I got hooked on stand-up. I didn’t know anyone who did stand-up, so this idea that you might be able to do it for a living was out of left field.”

In the following years, Spade found some success, moving to Los Angeles and landing small movie roles, including 1987’s “Police Academy 4: Citizens on Patrol.”

In 1990, he was hired by “SNL” as a writer/performer. It was there that he first met Chris Farley. The two bumped into each other in the lobby of the Omni Berkshire hotel in Midtown, where both newbies were staying.

Spade liked Farley immediately for not being a “cocky showbiz a - - hole,” and their now-familiar dynamic was present from the start.

“My job was to make him feel dumber than me,” Spade jokes.

On their walk to work that day, Spade cracked on Farley for refusing to withdraw more than $20 at an ATM, and for spotting a McDonald’s and naively pointing out that they had one back in Wisconsin.

The two became close friends, and would go on to make 1995’s “Tommy Boy” and 1996’s “Black Sheep” movies.

Spade spins a few Farley anecdotes in “Almost Interesting,” including a previously untold doozy about a copy of “Playboy” Spade once brought to the “SNL” offices to show off his new Playmate girlfriend. Farley stole the magazine then later left it on Spade’s desk – only a bit stickier, having pleasured himself on the pages.

“I could tell by the look on his face that he was suddenly worried he had gone too far,” Spade writes. “Chris had gone too far. He did every time. That’s what made him Chris.” Spade admits it’s sometimes a burden being the go-to guy to speak about Farley, who died in 1997.

“It’s hard for anyone to have questions all your life,” he says. “A lot of times it’s strangers, and they want to know things, and it’s very personal. It just keeps coming up. Most of the time, it’s perfectly fine.”

While Farley was a star virtually from his first day at “SNL,” Spade struggled.

“I didn’t know how to write sketches and I didn’t have tons of characters or impressions,” he says. “I was sort of an amusing person. I had to figure out how to make that pay off, and I was in a race to getting fired.”

One breakthrough came when Patrick Swayze hosted in 1990. One night, Spade spied the actor sitting alone in the writers’ room and tried to talk to him about an idea for a sketch. Swayze’s snippy publicist, however, suddenly appeared and barred Spade from entering.

“Oh, hi, just wanted to chat with Patrick for a second,” Spade said.

“Annnnddd youuu arrrrre?” the publicist responded.

“Oh, I’m sorry, I’m David Spade,” he replied.

“Right, and this is regardinggggggggg?” the publicist replied.

Ultimately, she refused to let Spade speak to Swayze, insisting he was “swamped,” despite the fact that the actor was sitting in plain view reading a magazine.

Spade ultimately mined the experience for a sketch about a snarky receptionist at Dick Clark Productions who fails to recognize MC Hammer. It turned out to be his breakout.

His other signature bit, “Hollywood Minute,” where the comedian ragged on celebrities from behind the “Weekend Update” desk, was born one day when Spade was making jokes while flipping through a copy of People magazine.

“That’s something I would do while waiting for the writers’ meeting,” Spade says. “Finally, [writer] Bob Odenkirk said, ‘Why don’t you just do that?’ ”

“Hollywood Minute” spawned perhaps the most infamous joke of Spade’s career. “Look, children,” he cracked beneath a photo of former “SNL” cast member Eddie Murphy, who at the time was coming off several Hollywood bombs. “It’s a falling star. Make a wish.”

“To Lorne’s credit, he never steers you away from [joking about] people,” Spade explains. “He’s very good about not coming in going, ‘Guys, Paul Simon is a friend. I think it would be better to [whistles].’ ”

The Monday after the joke aired, Spade was sitting in the writers’ room when an assistant appeared to tell him Murphy was on the phone down the hall.

“My heart stopped,” he writes. Spade told the assistant to take a message. Seconds later, the phone in the writers’ room rang. It was Murphy. Spade said to take a message, then went to talk to cast mate Chris Rock. Meanwhile, Murphy called again.

“You better call him,” Rock advised. “You don’t want him coming down here. Don’t forget, he’s still a black guy.”

Spade finally returned the call and Murphy screamed at him, “You dumb motherf – – ker! I’m off-limits, don’t you know that?”

The bad blood persisted for years, and Murphy has admitted the joke kept him from returning to “SNL.” He has never hosted since he left, and he was the only major cast member to skip the 25th anniversary special in 1999.

Recently, however, Spade spotted Murphy driving down a Beverly Hills street. Murphy rolled down his window and casually asked, “Hey, Spade, how are you doing?”

“My Watergate with Eddie Murphy was over,” Spade writes. The two also met at February’s 40th anniversary “SNL” show last spring.

“He was nice to me. He gave me a hug,” Spade says. “I don’t think he cares anymore. He can’t possibly.”

A story involving Spade’s ex-assistant has a less-happy ending. In 2000, the comedian awoke in his bedroom to find David “Skippy” Malloy standing over him. Malloy then attacked his boss, punching him and attempting to subdue him with a stun gun. Spade managed to get away and call the cops. Malloy was caught, but Spade refused to press charges.

“They said he’d only get three to six months, and he would probably leave in two days like Paris Hilton for Round 2, so I thought, what’s the point?” Spade says.

Spade writes that the animosity might have stemmed from Malloy being turned down for a role in 2001’s “Joe Dirt” — a part that went to Kevin Nealon instead.

Malloy still works in Hollywood as a production coordinator. According to IMDb, he’s currently on “Jane the Virgin.”

“The experience made me not cautious,” Spade says. “I still leave my door open. I’m just trying to live life and not be a freak about it.”

David Spade appears at the 92nd Street Y on Sunday and will sign copies of his book at Barnes & Noble Union Square on Monday.