Snippets of home movies reveal that they’ve been friends since childhood, BFFs forever growing up on a German island in the Baltic.

Now pushing 30 and living in Berlin, Paula (Cara Cult) and Jojo (Nina Gummich) still do everything together. Everything. Paula sees to that.

If she’s bored with whoever she’s hooked up with on a given night, she makes sure hers isn’t the only coitus she interrupts. Does she even know “grenzen,” the German word for “boundaries?”

Headstrong, rash and living in an almost permanent impulsive hissy fit, we wonder, as the Bee Gees sang, “How Deep is Your Love?” Because this isn’t a crush, isn’t an actual romance at all. It’s some sort of clingy toxic dependency that Paul has “For Jojo.”

Barbara Ott’s intimate, edgy film, based on a Stefanie Ren script, takes us inside a lopsided co-dependency as, we guess, it runs its course.

Cult, in that German shag haircut, leather, jewelry and sneer that’s become a Berlin Slacker Stereotype, ably turns Paula into a personal nuisance and a public menace.

Jojo leaves town for a stint of work in Mexico and Paula won’t leave her in peace to get her ticket to board. She spies a guy they grew up with in “Sh–sville,” on the island, and insults him repeatedly to his face. He’s flying to surf in Tulum, and Paula’s many, many calls to Jojo reveal that they’re hanging out and maybe falling in love.

Paula won’t stand for it. When they abruptly return together, Paula flips out at what they’re not telling her, stopping the shared car mid-bridge/mid-tantrum until they fess up.

When they drive Daniel (Steven Sowah) home with them, Jojo can’t stop insulting him and ignoring her doesn’t help. News that they’re already talking marriage reheats the ongoing meltdown. Jojo says she’s going back “home” with Daniel and Paula turns it up a few more notches.

“I give you guys two days,” she hisses (in German with subtitles, or dubbed into English). “Maybe until the weekend.”

So Paula is going “home” WITH them.

“I’m not letting you marry Daniel,” she declares.

Jojo ignores Maya Angelou’s advice — “When people show you who they are, believe them.” Bad move.

“For Jojo” isn’t some “Fatal Attraction” thriller. But for a non-violent drama it’s kind of brutal. The screenplay cooks up all sorts of ways for Paula — a narcissist who never thinks anything through — to sabotage this relationship that could cost her the best friend she’s been mooching off, leaning on and clinging to forever.

As Jojo is likely to say “Enough is enough” at some point, this is plainly a zero-sum game Paula is playing. We see it. She doesn’t.

Cult and Gummich plays these closer-than-sisters two in a way that makes every wedge Paula finds and every Jojo reaction to what she can see is happening in-the-moment believable.

The reasons for their deep bond are sketched in as Paula becomes completely unmoored in what is essentially a long tantrum of a movie. She uses people left and right, storms out of arguments and goes so far as sleeping on the beach to show her outrage.

Can this wedding be saved? What kind of a friend do you have to be to put up with that? We can only guess at the final straw, only speculate on the collateral damage.

And Cult, sullen and furious, manipulative and demanding, gives us as vivid a picture of toxic interpersonal dependency as we can stomach, never giving ground, crossing one line after the other until we’re screaming at her, Jojo, Daniel and the TV in indignation.

Rating: TV-MA, sex, nudity, profanity

Cast: Cara Cult, Nina Gummich, Steven Sowah, Louis Nitsche and Anne Zander.

Credits: Directed by Barbara Ott, scripted by Stefanie Ren. A Netflix release.

Running time: 1:35