About halfway through “The Last Kiss,” a remake of the 2001 Italian movie “L’Ultimo Bacio,” the action comes to a head. As friends gather following the death of one of their fathers, Jenna (Jacinda Barrett) is surprised to find Chris (Casey Affleck) but not her boyfriend, Michael (Zach Braff), since the two were supposedly out together. Until then, Jenna has seemed easygoing and unflappable; however, being pregnant and unmarried, she is more vulnerable than she lets on. As Chris stumbles to provide an alibi for his friend, Jenna grows suspicious. It turns out she has reason to be: Michael is at a frat party with Kim (Rachel Bilson), a flirtatious undergraduate who offers escape from thoughts of impending fatherhood and marriage.

When Michael returns home hours later, Jenna knows everything but the details. A screaming match ensues, and for a moment this movie, which during its first hour hops lazily from cliché to cliché, finds its heart at the height of its melodrama. Then Jenna inexplicably pulls a knife on Michael, and the viewer knows that once again the film’s woeful script has failed to provide the words to make a poignant situation believable. As if acknowledging this failure, Michael, who had rebuffed Kim earlier that evening, rushes to her dorm room to consummate the affair. The remainder of the film is a parody of regret, confession, and penance.

“The Last Kiss” is a movie about the crisis of turning 30, which, in our era of prolonged adolescence, amounts to the crisis of coming-of-age. Other than Kim and Jenna’s parents, all the principal characters are 29 and hopelessly confused. Chief among the lost are Michael’s three best friends, who seem less like actual people than stereotypes of different ways young men can suffer at the hands of women: Chris, who has lost his will in an overstressed, unsupportive marriage; Izzy (Michael Weston), the pathetic dumpee still stuck on an ex; and Kenny (Eric Christian Olsen), the womanizing relationship-phobe.

The other characters are barely more interesting.The day after her one-night encounter with Michael, Kim shows up at his workplace with a new mix CD in hand, as if to remind us that she’s just a college student. When Jenna’s parents’ marriage suddenly gets rocky (they’ve been together for 30 years, after all), the mother (Blythe Danner) runs to a former lover, who of course is now happily married.Jenna’s father, meanwhile, is one of cinema’s most tired stereotypes: the cold shrink who listens to his patients’ problems all day long but fails to recognize his own wife’s suffering. Thankfully, he is played by the ever-excellent Tom Wilkinson, who makes him the film’s most rounded personality.

Whom are we to blame for “The Last Kiss?” Some will point to the star, Mr. Braff. In “Garden State,” his last offering (which he also wrote and directed), he got away with awkward, empty stares because his character seemed dreamy; here, the same act comes across as merely disengaged. But the real mastermind of this bomb is writer Paul Haggis, fresh from striking gold with the Oscar-winning “Crash.” In what could have been a challenging film about extended adolescence and the real difficulty of moving beyond it, he has characters offer pearls of wisdom like: “College was the best years of my life”; “When you graduate, no one cares about your GPA”; “Woman are complicated, men are easy”; “I feel like my whole life is planned out before me”; “I’m your last chance at happiness”; and “It’s what you do to the people you love that matters.” Sound familiar?

But the failure of “The Last Kiss” is not limited to its inert dialogue or warmed-over story. As in “Crash,” the film seems to think it can make do without realistic personalities, since its characters are meant to represent types of behavior, to fill slots in the plot. After Jenna is betrayed, she acts like the generic hysterical woman who’s been wronged, not like Jenna. Michael’s friends plan a long road trip to Patagonia, in part it seems, because that’s the sort of thing confused 20-somethings do. Even Michael’s supposed crisis, that gnawing anxiety that drives his doubt and infidelity, feels like an invention — the poor writing is simply unable to bring the particularity of his crisis to life.

When Kim bumps into Michael at a wedding in the beginning of the movie, the encounter is meant to be something of a mini-crash. But there is no electricity, no chemistry. At first, Michael is confused by her interest; later, he’s bemused. That a young man in a committed relationship and expecting a baby would have an affair with a girl he met at a wedding is entirely believable, as is the fact that he would have it with someone he wasn’t that interested in; similar stories have driven powerful movies in the past. But not these two, not the way it happens. “You make me feel 10 years younger,” he says when they kiss. “You’re making me lose my mind,” she responds. The words are entirely unconvincing, and not only for me. Watch the actors. They don’t buy it, either.