Zoe Chao puts on a clinic on “the funny new BF of the leading lady” as a rom-com trope in “Your Place or Mine,” an exceptionally mild-mannered farce set up as a Reese Witherspoon/Ashton Kutcher vehicle.

Chao plays the pretty, narcissistic and rich neighbor-with-benefits to Kutcher’s character who barges in on his best friend (Witherspoon), who has done a housing swap for a week so that she can be in New York to take an accounting class.

“Accounting” does a lot of the heavy lifting in this comedy. No, that’s not a good thing.

But every time Chao’s minx Minka appears and imposes herself on Debbie, funny words tumble out of her unfiltered mouth in that ever-so-special Zoe Chao way. She snaps, crackles and pops around Witherspoon, no slouch at comedy herself, delivering “Mom wardrobe” putdowns with a New York edge and a hint of “Aww, honey” pity.

“I am not...” single mom/school accountant Debbie begins.

“Human! We know,” Minka blurts. “Don’t make me sing “I Am a Woman in Love” by Barbra Streisand, because I will. I sang it at my Nana’s retirement home!”

Listen to the six different single-syllable corrections Chao flings at her new friend about what she’s feeling and what she should do about this situation that Debbie’s meddling and snooping around her male friend’s penthouse created.

“NO! No. No? No. NO no…No!”

If Golden Globe winner Jennifer Coolidge’s brand is “MILF,” Chao’s ascended to “BILF,” no doubt about it. And for her to steal this movie from the leads, when the great Tig Notaro is also on the court is a straight-up baller move.

Witherspoon and Kutcher play friends who hooked-up in college. Once. She was going to be an editor. He was dreaming of life as a novelist.

“Twenty years later” they’re still connected, besties who “tell each other everything,” which becomes one of the film’s two running gags.

She’s settled into divorced motherhood in a house ever-practical Debbie bought in her 20s. Debbie gave up her dream, taking up accounting to support her now 13-year-old son (nepo baby Wesley Kimmel), micromanaging his life as well as hers because she’s invented “Saran Wrap parenting.”

That’s what her college pal Peter (Kutcher) labels it. But he’s given up his dream as well. He’s some sort of rich “consultant” (the lazy screenwriter’s best guess at what career would pay for a penthouse), “just a lonely guy with outstanding hair.”

They’re both in their ’40s, still tight. But events contrive to keep her from visiting him in NYC for a week while she takes a qualifying seminar and test to advance her accounting career prospects. He grabs the chance to perform the Big Gesture, tells her to keep her travel plans. He’ll fly to LA and babysit and “parent” her allergic-to-everything, sheltered and coddled kid.

Remember those “two running gags” mentioned above? The first is Peter’s lifelong obsession with The Cars. Their music fills his ringtones, his drive-to-work music, his life. The way the unsubtle writer-director withholds it, any casual Cars fan KNOWS which song is being saved for the Big Finale.

The second running gag is how “tell each other EVERYthing” Debbie finds all these things out about Peter’s life, that he wrote a novel, for instance. With instant pal Minka egging her on, Debbie decides to read it and get it to a publisher.

Peter? He’s finding out the degree of Debbie’s smothering of her son he only suspected, that she has some rich doofus neighbor (Steve Zahn, another scene-stealer) who has made her hillside garden his life’s work, thanks to his crush on the pretty Accountably Blonde.

To say writer-director Aline Brosh McKenna, who scripted “Morning Glory” (Meh.) and “The Devil Wears Prada,” never deviates from “the obvious” here is really an understatement. When we hear Zahn’s character run through some “how I have the time and money to garden for her” palaver, we might have a moment’s pause that he’s just BSing Peter and us. But that would imply complexity and nuance that no character in “Your Place” displays.

McKenna realized she hit the Netflix jackpot when she scored an Oscar winner and Kutcher for her leads, and phoned it in from there. They have just one scene together, and it shows what passes for heart and chemistry, and comes entirely too late to make a difference in the movie.

But Notaro, playing a character not even outlined, much less “sketched in,” makes middling lines funny. Zahn turns a sight gag into an amusing distraction.

And Chao cases the joint, procures something to pick the bicycle-lock of this simple scenario, and steals it. She had to know that on an all-star time-killer with such limited ambitions and laughs, nobody would make a fuss over petty theft.

Rating: PG-13 (Brief Strong Language|Suggestive Material)

Cast: Reese Witherspoon, Ashton Kutcher, Tig Notaro, Wesley Kimmel, Steve Zahn and Zoe Chao.

Credits: Scripted and directed by Aline Brosh McKenna. A Netflix release.

Running time: 1:49