“Her and I have this witty banter thing,” single-mom Kim (Krysten Ritter) blurts out to her date as a way of explaining a little verbal snit-fit she’s shared with gal-pal Deena (Kate Bosworth. “It’s nothing serious.”

There’s fact and fiction in that bit from the preciously titled single-mom rom-com “L!fe Happens.”

No, the banter isn’t very witty. But yes, this is “nothing serious.”

“L!fe” gathers a trio of Hollywood’s most adorable pushing-30 hotties, makes them roommates struggling to get their careers in gear and men in their lives, and makes one of them that accidental single mom.

It’s a sitcom pilot waiting for re-write.

An opening scene has Kim and Deena lightly bickering over the last condom in the house. Guess who loses that argument?

A year later, Kim is struggling to get by as a dog walker in the employ of the rude and (allegedly) funny Francesca, a dog-loving, baby-hating harridan who will probably never invest in Kim’s big idea — a “dog mall,” filled with stores that cater to dog folk. The no-nonsense Deena is pitching a no-nonsense advice-to-the-lovelorn book and writing a column on that in LA Weekly. And their ditzy, virginal roomie Laura (Rachel Bilson) contemplates job ofers from bikini car-washes and “naked human sushi platter” restaurants. Because she’s cute and scantily clothed.

There’s a frothy unreality to all this, from the gorgeous house this trio stays in, to their staggering collection of high heels and designer short skirts. The movie makes no effort to explain why or how seemingly shallow and self-absorbed Kim came to carry this pregnancy to term. It’s as if the movie is in denial of the “truths” the script lays out there.

Kim is a lost and lovelorn mom — utterly inept — who gets no help from the toddler’s Aussie surfer dad. But Laura, Deena and friend-to-indie-film Seymour Cassel (grandpa) are there for babysitting duty.

The movie is about Kim’s coming to terms with this sudden mothering thing, thanks to the lie she tells a cute guy (Geoff Stults, Ritter’s “She’s Out of My League” co-star). She passes the baby off as Deena’s, because banal but cute guy says, “Kids, what a buzzkill, huh?”

The cast is cute and sitcom ready, with Bosworth being the big comic surprise. She gives Deena a brittle edge and high-speed man-bashing/man-trapping patter that rides the razor’s edge of post-feminism. Justin Kirk, the funniest thing about TV’s “Weeds,” plays a pretentious loon “best friend” to the leading man and lands most of the laughs here.

But there just aren’t many of those. To a one, every character is so wrapped up in him or her self that there aren’t any real sparks between anybody. And there is nothing new to this “Gosh, babies are hard” message, especially since the movie doesn’t make is case very convincingly.

Ritter co-wrote it with “Funny or Die” online video vet Kat Coiro, who directed. They know how to write a script that will convince friends and former colleagues (Jason “American Pie” Biggs” has a glorified cameo) to pitch in with them. It’s giving them something to play and say that trips them up.

MPAA Rating:R for sexual content including references

Cast: Krysten Ritter, Kate Bosworth, Rachel Bilson, Geoff Stults, Justin Kirk, Jason Biggs

Credits: Directed by Kat Coiro, written by Krysten Ritter and Kat Coiro, a PMK/BNC Release.

Running time: 1:40