Struggling musician Peter Bretter (Jason Segel) sneaks up on his ex-girlfriend after she shows up at the same Hawaiian resort he went to in an effort to ease the pain of their breakup in Forgetting Sarah Marshall.

Universal Pictures / Glen Wilson

Billed as “the world’s first romantic disaster comedy,” Forgetting Sarah Marshall is a sometimes funny, sometimes uncomfortably icky movie about a schlub who thinks his life is ruined when he’s dumped by his TV star girlfriend.

Jason Segel, who wrote the film and stars as down-in-the-dumps TV music composer Peter Bretter, makes pointed and too-true observations about the pain and loss suffered when, out of the blue, a long-term relationship goes kaput. And he makes it more palatable with a thick layer of no-holds-barred humor.

Heartbroken Peter, facing a meltdown, at first tries to jump right back into the dating game as a way of forgetting Sarah Marshall, the star of a crime-scene TV show. But those one-night-stand relationships lead nowhere, especially with Peter breaking into uncontrollable sobs at what should be the height of passion. When that leaves him feeling just as empty and ever-weepy, he takes a spur-of-the-moment trip to Hawaii to cheer himself up. But his attempt at peace and paradise quickly go down the drain when he discovers that Sarah and her new boyfriend, self-centered English rock star Aldous Snow (Russell Brand), are staying at the same resort hotel.

Forgetting Sarah Marshall often seems a cross between the bald-faced comedies of director-producer Judd Apatow and the Farrelly Brothers’ remake of The Heartbreak Kid.

No surprise on the Apatow front. Apatow, who directed The 40-Year-Old Virgin and last summer’s outrageous Knocked Up and produced the even more outrageous naughty teens hit Superbad, is the co-producer of Forgetting Sarah Marshall, as well as being Segel’s mentor. So the film, directed by Nick Stoller, another Apatow protégé, has all the earmarks of an Apatow production, right down to Jonah Hill, who co-starred in all three previous Apatow hits and here plays an ingratiatingly nebbishy waiter.

Like Katherine Heigl’s character in Knocked Up, who had a sounding board in her sister and brother-in-law in the film, so Peter has his brother Brian (Bill Hader) and sister-in-law Liz (Liz Cackowski), who keep turning up, usually in Internet messages, to offer sometimes unwanted advice. Forgetting Sarah Marshall has lots more sex and nudity than Knocked Up (though not as much profanity). A memorable early scene finds Peter naked, both physically and emotionally (and front and rear), while the perky blond Sarah (Kristen Bell, TV’s Veronica Mars) tells him their six-year romance is dead in the water.

But there are echoes here, too, of The Heartbreak Kid, in which a new husband tries to dump his wife on their honeymoon at a Mexican resort after falling for another guest. That film was dumped on by many critics, who found it a tawdry rewrite of the nearly forgotten 35-year-old original and had little sympathy for the beastly actions of the husband toward his annoying, yet oddly sympathetic bride.

No such problems in Forgetting Sarah Marshall, where Peter is the wronged party … or so he sees it. Peter’s constant weeping and hissy fits are played for laughs, but get carried almost to annoyance as he can’t seem to get on with his life. The film is about learning to let go and to grow up. Peter, who appears to be in his early 30s (Segel is actually 28), seems a bit long in the tooth for such childish histrionics.

Nevertheless, there are lots of funny doings in Forgetting Sarah Marshall, including the situations that keep putting Peter, Sarah and Aldous in close proximity, such as when Peter gets seated at a table next to theirs in a restaurant. That Brand seems to be channeling Johnny Depp at his most flamboyant Capt. Jack Sparrow moments only adds to the fun.

But Peter has been tossed a lifeline by Segel in the lovely Rachel (Mila Kunis), the resort’s customer-relations rep, who takes pity on the heartbroken, heart-on-his-sleeve lug and eventually tries to pull him out of his grand funk with something more than just an upgraded room and a piña colada. Kunis makes Rachel a sensitive, sweet dreamboat, at least until an uncomfortable moment in which she turns into a raging lioness at the sight of her ex-boyfriend. Oof! Where did that come from? A lot of good will toward her is lost in this scene. But some of it is regained later, especially in a “battle of the sexes” moment when the two couples find themselves in adjoining bedrooms trying a bit of boudoir one-upmanship loud enough to penetrate the thin walls between.

Forgetting Sarah Marshall is a dizzying, uncompromising look at modern romance, both busted and on the mend. It’s not for the easily shocked, however. Make sure you stick around as the credits begin at the end and you will be rewarded with a very funny update of exactly where Sarah’s TV career is headed.

*** 1/2Forgetting Sarah Marshall

Starring: Jason Segel, Kristen Bell, Mila Kunis, Russell Brand, Paul Rudd, Jonah Hill, Bill Hader, Mack McBrayer.

Rated: R, contains sex, nudity, profanity, adult themes.

mjanuson@projo.com