How do you get actor Andrew Garfield — Tony Award winner, former Spider-Man — to tap into his inner Johnny Knoxville?
Have the real guy on hand, said director Gia Coppola.
The “Jackass” series creator plays a small role in Coppola’s new movie, “Mainstream,” out Friday, which stars Garfield as a charismatic drifter who becomes an internet sensation. For some of the film’s biggest scenes, Coppola tapped Knoxville’s pranking advice. “That’s really his art form,” she told The Post over Zoom. “And so much of the content in this [current internet] world is an homage to ‘Jackass,’ creating these kinds of stunts.”
Hence, she features one scene in which Garfield’s character runs down a major LA street, wearing a fake penis — and not much else.
“Originally, this was written as a much tamer stunt,” she said. “But I asked Andrew, ‘Would you be down for doing this on Hollywood Boulevard?’ And he was like, ‘Hell, yeah!’ And then he went further and decided to add a prosthetic d - - k, instead of us just blurring out nude underwear.”
This is the second film from 34-year-old Coppola, whose family name is synonymous with moviemaking: Her grandfather is Francis Ford Coppola, and her aunt is Sofia Coppola. Nicolas Cage is one cousin of many.
Her sophomore film, after 2013’s “Palo Alto,” sees Garfield’s mysterious, hyperenergetic character intersecting with an aspiring filmmaker (Maya Hawke of “Stranger Things”) and becoming her muse. Their YouTube collaboration with her writer best friend (Nat Wolff of “The Stand“) ends up bringing them fame, and the insanity that can come with it. “I was excited to have someone like Andrew, who is typically cast as the hero, for this character who’s wild and big and crazy,” Coppola said. “To let him run free and experiment with it.”
In another scene, Garfield’s character, who calls himself No One Special, appears on a panel of real-life personalities, including infamous YouTuber Jake Paul, Japanese model and TV personality Rola, and makeup artist Patrick Starr. What none of them knew, apart from Knoxville as the scene’s fictional host, was that Garfield planned to freak out, jump up on the table and appear to use it as a toilet.
“We cut out that part in the script,” Coppola said she told Paul and the others. “We only had one opportunity to really try and surprise them. It was fun to have Knoxville around to figure out how to execute it.”
Reactions to the meltdown varied wildly. “Rola’s gut reaction was just to stay there. Jake Paul pulled out his camera. And Patrick just bolted.”
Coppola also cast her cousin Jason Schwartzman, as a sleazy agent to the trio. Behind the camera, she said, he was a font of support. “Jason is hilarious, he’s nonstop. I ask questions, and he just runs wild.”
As for the director’s feelings about online culture, she can sum it up in one scene: “When Maya’s character throws up [animated] emoji, that was how I was feeling. Inundated with content. I really needed to get it off my chest.”
After the vicarious cinematic purge, she said she feels much better. “My relationship with social media has really been relieved!”