When Diane Keaton is misused, it’s lame and depressing.

To know Diane Keaton is to look back at her previous films, including her Oscar-winning role in “Annie Hall,” her sweet, comical side in “Father of the Bride” and “Something’s Gotta Give,” and as Kay Adams in the first two “Godfathers.” The people who made “Love the Coopers” and “Book Club,” in recent memory, know nothing about her talents, and practically tainted her ego. This is why I skipped “Poms” and “Love, Weddings & Other Disasters.”

Her next movie is “Mack & Rita,” which is yet another lousy attempt to mimic “Big.” The last movie to try and fail in that notion was the age reversal with Regina Hall transforming into her younger self played by Marisa Martin in “Little.” “Mack & Rita” has Keaton playing the older version of a young woman, who has always felt she was in the body of an old woman. She wants to dress and act like one, while trying to fit in with society.

Elizabeth Lail plays Mack, a struggling writer with a dopey boss (Patti Harrison) and a dog named Cheese. You know like Mack-and-Cheese. Her lesbian BFF Carla (Taylour Paige) is getting married, and they spend a weekend in Palm Springs, where she comes across a tanning bed, or “regression pod” as Luca (Simon Rex) calls it. He tells Mack to relax and think about who she wants to be, and when she comes out of the pod, she’s now in the form of Diane Keaton.

This is when the blandness and stupidity kick in.

When the now elderly Mack arrives at the rental house her bachelorette gals are staying at, Carla has to threaten her with an empty pepper spray, and shout “Ghost! Ghost! Ghost!.” I think Marcedes Ruhl did a better job misinterpreting her boy being kidnapped by who was actually his adult self in “Big,” whereas Paige is aggravatingly wasted, and she was wonderful in “Zola.”

Then, she learns it’s Mack on the inside, while their dopier friends (Aimee Carrero and Addie Weyrich) can’t know it’s Mack as the old lady. And that’s why she has to fall in the pool, as if it was supposed to be funny.

Once again, the movie acts like it hasn’t even seen “Big” or at least even taken its important and heartfelt message. If “Scream” can give people the rules of surviving a horror movie, then why can’t we get somebody to make a movie about surviving a body swap or an aging comedy?

So, since neither Mack nor Carla want to teach anyone about surviving this kind of fantasy, Mack has to pose as her Aunt Rita, hence the title “Mack & Rita.” She earns the obligatory friendship with Carla’s mother’s (Loretta Devine) and her wine club gals (Wendie Malick, Lois Smith, and Amy Hill), and uses this fantasy to connect with her dog walker and crush Jack (Dustin Milligan).

Just when things have to be generic, Mack uses her Rita look to give herself a big name on Instagram, getting paid to post pictures at lavish parties.

Or how about when she takes magic mushrooms, and sees her dog speaking with the cameo voice of Martin Short, using his “Father of the Bride” accent? It might be promising, but it’s handled all lackluster.

“Mack & Rita” isn’t playing in a lot of theaters and that’s a good thing, because you people deserve better than this boring, stupid, weak, and insipid comedy that knows nothing about this genre or Keaton or any of these fine talents, who have done better than succumb to all these bad jokes. When her new old friends find out the truth about her, the Malick character has to say: “I need another refill.” And Harrison, who gave a career best performance in “Together Together,” is acting like she can’t act. She can act in other movies, but for some reason, she talks like some kind of Kardashian jerk.

Keaton has always been a wonderful actress, but in recent years, only her voice acting roles in “Finding Dory” and the “Green Eggs & Ham” series have been surviving the new generation. In the real world, she’s given some very bad material, and the amazing thing is that Keaton also produced “Mack & Rita.”

Do yourself a favor. See “Annie Hall,” not this.

Categories: comedy