Producers:  Alex Saks, Diane Keaton, Stephanie Heaton-Harris, Jina Panebianco and Dori Rath   Director: Katie Aselton   Screenplay: Madeline Walter and Paul Welsh   Cast: Diane Keaton, Taylour Paige, Elizabeth Lail, Loretta Devine, Dustin Milligan, Simon Rex, Amy Hill, Lois Smith, Wendy Malick, Patti Harrison, Addie Weyrich, Aimee Carrero, Nicole Byer, Martin Short, Molly Duplass and Catherine Carlen     Distributor: Gravitas Ventures

Grade: C-

Diane Keaton keeps plugging away even as the material she’s been offered over the last two decades has gotten steadily worse.  The latest example is this frantically unfunny body-switch comedy that might just make you want to switch theatre auditoriums or streaming services.  “Mack & Rita” is a comedy about mixed identities that delivers messages as mixed-up as its characters.

MacKenzie, or Mack, Martin (Elizabeth Lail) is a thirty-year old writer who’s not just shy and reserved but feels out-of-place among her pals Carla (Taylour Page), Sunita (Aimee Carrero) and Ali (Addie Weyrich).  They all love the stuff people their age are supposed to, but she doesn’t: as a child (played by Molly Duplass in flashbacks), she idolized her free-spirited grandma (Catherine Carlen), who was always true to herself despite what other people thought, and wants to emulate her example; Mack’s only book, in fact, is a series of essays on her grandmother.  But she feels trapped by expectations that she should act like her friends do, rather than the older woman she feels herself to be.  And her cynical agent Stephanie (Patti Harrison) prods her to concentrate on the influencer gigs she arranges for her, rather than trying to write, since she says nobody reads anymore.

Mack gets a miraculous chance to live her dream when, on a trip to Carla’s bachelorette party in Palm Springs, she decides to visit a “life-regression” tent run by a goofy guru named Luca (Simon Rex) and emerges from his converted tanning bed as her seventy-year old self (Keaton).  Understandably upset at first—cue some of the actress’ screaming shtick—she convinces understanding Carla of her predicament and, assuming the identity of Mack’s Aunt Rita, quickly bonds with her friend’s feisty mom Sharon (Loretta Devine) and her klatch of equally spunky friends (Wendy Malick, Lois Smith and Amy Hill).

Released from her inhibitions, Mack-as-Rita, with Stephanie’s encouragement, turns a single viral post into social media celebrity and internet stardom, with all the financial benefits that entails.  She also returns home to spark a romantic relationship with her dog-sitter Jack (Dustin Milligan), a still-boyish guy who’s always been infatuated with Mack but whom her younger self kept at arm’s length because of her nervousness.  Naturally in the end Rita turns back into Mack, but with newfound confidence and the determination to—and this is the movie’s message—live like the person you really are.

Keaton infuses Rita with amazing, if misplaced, energy.  The exuberant upgrading of her wardrobe to go kookily flamboyant in ways that mirror the star’s cherished look is a relatively restrained bit of business compared to episodes in which her willingness to engage in knockabout farce is fully in evidence—a slapstick encounter with a pilates machine she’s meant to publicize as exercise for oldsters; a hallucinatory trial of shroom tea, which finds her prancing about in hippie-style dancing before collapsing on a bed and conversing with a dippy version of her dog Cheese (voiced by none other than Martin Short); a “happening” hosted by a woman called Urth (Nicole Byer) that ends with Rita’s wig literally catching fire.  (The last causes a rupture with Carla, since it prevents Rita from attending her rehearsal dinner, though Mack’s continued absence goes unremarked.)

In other words, this becomes an anything-goes, scattershot comedy that never settles on a coherent point of view and in which there are far more hits than misses.  You have to admire Keaton’s commitment, even while deploring the over-the-top nature of the performance she gives under actress Katie Aselton’s excessively indulgent direction.  The rest of the cast is agreeable enough, with Devine’s sass, Harrison’s caustic practicality, Rex’s oddball manner and Milligan’s likability especially notable, and it’s always fun to see gals like Smith, Malick and Hill doing their shrewd old lady stuff.  (Lail, surprisingly, makes little impression.)  The problem is that the dialogue provided them all by Madeline Walter and Paul Welsh rarely rises above the level of a mediocre sitcom.

The movie even looks pallid, except for Allyson Fanger’s extravagant costumes.  Tracy Dishman’s production design is variable, and Sean McElwee’s cinematography nondescript, while Michael A. Webber’s editing is as slapdash as Aselton’s direction and Leo Birenberg’s score is overemphatic.

One may admire Keaton’s determination to keep working, and working hard.  But a movie like “Mack & Rita” isn’t worth the effort.