Six years ago Brian Koppelman overheard a conversation that inspired a movie.

The co-director of “Solitary Man” was in a park in Manhattan when a man in his late 50s asked his grown daughter not to call him “Dad” because it made it too hard for him to pick up girls.

“It got me so annoyed and angry that I just started writing,” says Koppelman. “I thought it was really funny and really dark. This guy was articulating something on the surface that represented everything that was below.”

Koppelman quickly finished the first 20 pages of a script and showed them to his close collaborator and co-helmer David Levien.

The two have been friends since their teens and seldom work separately, but in this case Levien thought Koppelman should fly solo. “When Brian showed it to me I thought the voice was so intact and clear that if I jumped in it would be interference,” he says. So, among other projects, Koppelman completed the script that became “Solitary Man.”

In the film, which they helmed together, Michael Douglas plays the fictionalized version of the man in the park, a character reminiscent of many powerful businessmen the Long Island-bred duo grew up around.

“We were fascinated by the way they carried themselves,” says Koppelman. “They were like kings of the world, and from their business success they inferred that they had acumen in all other areas. But as you watch them age you realize it’s a big lie.”

Koppelman and Levien are the ultimate directorial collaborators, and — yes — they complete each others’ sentences.

“In pre-pro, we’re together in every meeting, every scout, making all the decisions,” says Levien. “We often ride to the set together.”

“And we both work with the storyboard artists,” says Koppelman. “We go over the shot list together the night before.”

Hiring the film’s department heads is a joint activity. “We interview everybody together,” says Koppelman. “Generally we have the same opinion of a person’s work.”

Cinematographer Alwyn Kuchler, who was recommended by Steven Soderbergh (one of the film’s producers), was at the top of their list, but he was unavailable at first and the co-helmers interviewed nearly a dozen other d.p.’s before Kuchler was able to rearrange his schedule. “He has the perfect esthetic for this film,” Koppelman says.

They also had their hearts set on Tricia Cooke to edit the film, especially because she had helped edit some Coen brothers’ pictures.

“We’re giant fans of their movies,” says Koppelman. “We thought it would be useful that Trish had spent time cutting movies with two directors. She’d be used to having two guys at her ear at the same time.”

When Cooke came on board she brought along another bonus: She happens to be married to Ethan Coen. The younger half of the sibling team ended up watching a few cuts of “Solitary Man.” “He gave us some terrific notes,” says Koppelman.

Signings & Bookings

Dattner Dispoto has scored two new d.p.’s: Christian Berger (“White Ribbon”) and Nancy Schreiber (“Serious Moonlight”).

Gersh bookings: production designers Giles Masters on Michael Brandt’s “The Double” and Claude Pare on Rupert Wyatt’s “Caesar: Rise of the Apes,” Richard Bridgeland Fitzgerald on Craig Gillespie’s “Fright Night,” J. Michael Riva on Marc Webb’s “Spider-Man,” Aran Mann on Aimee Mann’s “The Fields,” Michael Shaw on Showtime’s “The Big C” and Cory Lorenzen on ABC Family’s “Greek.”

Paradigm d.p. bookings: Alexander Gruszynski on Tyler Perry’s “For Colored Girls Who Have Considered Suicide When the Rainbow Is Enuf,” Sam McCurdy on Joe Lynch’s “Knights of Badassdom,” Kenneth Zunder on Artie Mandelberg’s “Killing Karma” and David Klein on Billie Woodruff’s “Honey 2” and Buzz Feitshans IV on Fox’s “The Good Guys.”

Additional Gersh bookings include costume designers Jacqueline West on Francis Lawrence’s “Water for Elephants” and Tom Broecker on Showtime’s “The Big C”; d.p.’s Jimmy Lindsey on Aimee Mann’s “The Fields” and Paul Sommers on CW’s “Vampire Diaries”; editors Sunny Hodge on Showtime’s “The Big C” and Jeff Gourson on TBS’ “In Security.”