If only they had trusted the original concept, based on screenwriter Paula Pell’s real life return to her parents’ home to get her stuff so the house could be put on the market. (You can see Pell in the film — she’s the one gagging in a brief appearance at the beginning.)

There’s a lot of comedy to be mined there, the bittersweet sort through the flotsam and jetsam of childhood and adolescence, the inevitability of the “What were we thinking!” moments as we look through old clothes, photos, and diary entries, and the sister dynamic, too, with the closeness and understanding only people who lived in your home and shared your parents have — and the competition and instant return to juvenile emotions that sometimes brings.

Fey and Poehler tried to add some interest by switching the roles from their last collaboration, with Fey as Kate Ellis, the wilder, less responsible sister, a beautician single mother with a teenaged daughter and Poehler as Maura Ellis, a compassionate nurse with a one-eyed rescue dog, divorced for two years and still feeling bruised and insecure.

The Ellis parents (James Brolin and Diane Wiest) have moved into a condo in a retirement community and want the girls to clear out their old room. They hate the idea of giving up the house, and so decide that what they need is one last big, wild party, like the “Ellis Island” parties Kate gave in high school. Kate pushes Maura to invite a handsome handyman neighbor (Ike Barinholtz, the moral and emotional center of the film and please put him in many more movies right now) and somehow he consents. Though Maura’s behavior around him is weird and off to the point of being disturbing, but for some reason he finds it appealing. They do not invite Kate’s old mean girl rival, Brinda (Maya Rudolph, one of the other bright spots), but she shows up anyway, on the policy that if you can’t beat ’em, join ’em, and if you can’t join ’em, call in a noise report to the police.

The fun includes the inevitable dance number and trying on clothes montage and some brief appearances by John Cena and “Crazy Ex-Girlfriend’s” Santino Fontana.

Here’s what’s not so fun (potential spoiler, but it’s in the trailer): a character falling backwards on a sharp, pointed object that gets lodged it his rear end for a supposedly hilarious scene of extraction that seems to go on forever, lots of humor about how getting drunk or smoking weed or having sex with someone you’ve just met is a sign of liberation, a guy who makes endlessly corny “jokes” so we are supposed to laugh at him for it, a mother whose teenager has to explain that it should not be her job to be the grown-up, condescendingly mistaking a construction worker for a homeless guy, condescendingly mistaking a nail technician for an oppressed person who never has any fun, a joke about “c–kblocking our parents,” and humorous ingestion of some very strong drugs. It’s more slumber party skit than movie, too slight for its running time and beneath the talents of America’s sweethearts.

Parents should know that this film has very explicit and crude sexual references and situations, gross-out comedy and graphic images, sexual situations, drinking and drug use, comic and slapstick peril and violence

Family discussion: Was there a house you were sorry to leave behind?  Why was it hard for Kate to do what her daughter wanted?  

If you like this, try: “Baby Mama” with Fey and Poehler