As Comic-Con fanboys and fangirls roared in excitement Saturday at Marvel’s Hall H panel, which featured the entire cast of “The Avengers: Age of Ultron,” one of the most popular films of the past 20 years was quietly discussed for a much smaller, attentive crowd at the San Diego Convention Center.

Director David Fincher, making a rare public appearance, sat and talked at length about 1999’s “Fight Club” with author Chuck Palahniuk — discussing everything from the story’s genesis to the project’s surprising marketing challenges, giving fans more insight on the cult film as it nears its 15th anniversary in October.

Though the movie, starring Brad Pitt and Edward Norton, is highly regarded today, it struggled mightily out of the gate.

“‘Fight Club’ sold less than 5,000 copies,” Palahniuk said of the 1996 book.

But Fincher, coming off the acclaimed and commercial hit “Seven” at the time, said he was immediately addicted to the novel. “I read it and couldn’t stop laughing,” he said. “Who the fuck doesn’t want to see credit card companies blow up?”

The feature adaptation of “Fight Club,” co-starring Helena Bonham Carter and Meat Loaf (or “Bitch Tits” as he was called in the film), was also a major disappointment at the box office in 1999 and received mixed reviews from critics.

Fincher, then 37 years old, said the risky project ultimately died at the box office because of false advertising, mostly from its distributor 20th Century Fox.

“Fox marketed ‘Fight Club’ mostly on the World Wrestling Federation. That’s when I knew we were doomed,” he said. He joked that the film was too “homoerotic” for WWF.

But it eventually paid off, as the director pointed out, saying, “‘Fight Club’ sold 13 million DVDs. It paid for itself.”

Bringing “Fight Club” to life onscreen, though, was not without challenges, even with star Brad Pitt on board to play Tyler Durden.

“Men don’t want to see Brad Pitt shirtless, and women don’t want to see him fighting,” Fincher said.

Fincher also noted that one person behind the scenes wanted to remove one of the film’s most iconic elements: the voiceover by Edward Norton.

“They wanted to make ‘Fight Club’ without a voiceover,” Fincher revealed. “So I fired that producer.”

It all worked out for the film, though, but Fincher says many people don’t “get” the message.

“‘Fight Club’ is about moving through a modern disconnected society,” Fincher said. “It’s a satire. Many don’t get that.”

"People offend waaaaay too easily." Fincher on audiences who watched FIGHT CLUB at test screenings. #sdcc — Chuck Palahniuk (@chuckpalahniuk) July 27, 2014

Still, even the director has qualms about the movie’s fans.

“My daughter had a friend named Max. She told me ‘Fight Club’ is his favorite movie,” he said. “I told her never to talk to Max again.”

For his part, Palahniuk revealed the genesis for the novel that spawned it all.

“I noticed if you looked bad enough, no one asked you what happened,” he said.

Palahniuk recently announced that he’s developing a 10-issue max-series sequel to “Fight Club” for Dark Horse Comics, picking up 10 years after the novel left off. It’s set for release in April.

Fincher, whose next film “Gone Girl” is also based on a dark novel, summed up Palahniuk’s now-famous work in one sentence before heading off into the night.

“‘Fight Club’ is about the most dangerous thing in the world — ideas.”