How do you forget someone you can’t escape? You can’t. But Forgetting Sarah Marshall, for all its tortured breakup hardships and indecent exposures, makes us laugh long and hard enough to forget we’re watching a sad man painfully try to move on.

That man’s name is Peter (Jason Segel), and at the beginning of Nicholas Stoller’s (writer of Fun with Dick and Jane) film he’s unceremoniously dumped by Sarah Marshall (Kristen Bell), the star of a CSI-like TV detective drama. For solace Peter seeks the comfort of other women and the advice of his brother (Bill Hader), but the constant stream of ads for the TV show doesn’t allow thoughts of Sarah to escape him. To get her out of his mind, he decides to go on vacation in Hawaii.

Big mistake. Upon arrival he meets a cute receptionist named Rachel (Mila Kunis), but to his misfortune he soon sees Sarah there with her new boyfriend, rock star Aldous Snow (Russell Brand). Awkward and amusing encounters ensue, and layers of truth that bring a new, fresh perspective to what could have been an ordinary romantic comedy are cleverly revealed.

One more note on the breakup scene. Peter is naked throughout, and refuses to cover himself. Metaphorically he’s vulnerable and completely exposed, and thanks to a few close-ups of his not-so-flaccid penis, he’s literally exposed as well. The scene plays for laughs – for whatever reason, male genitalia always elicits laughter – but it’s also quite somber, and Peter is enough of a loveable loser to pull it off convincingly.

Segel, who also wrote the script, has the look and disposition of an average Joe, which allows the audience to identify and empathize with him. If he was better looking the story wouldn’t work because we’d constantly wonder why he was so hung up on Sarah when he could ostensibly have his pick of eligible women. But with a slightly flabby body and ordinary features, we quickly get the impression that Sarah was out of his league from the get-go, and yet loved him anyway during their five years together. Fortunately, because Segel is so likeable and funny the movie never falters.

The film was produced by Judd Apatow, who is single-handedly redefining immature guy humor one movie at a time. Apatow mainstays Paul Rudd and Jonah Hill are highly amusing here as a burnt out surfing instructor and overly-attentive waiter, respectfully, and newcomer Brand gives unexpected depth to an otherwise typical rock star lothario.

Although some of Apatow’s movies (Drillbit Taylor) miss the mark, others (he directed The Forty Year-Old Virgin and Knocked Up, and produced Superbad) reflect the smart, new age humor that has made him and his minions the new kings of comedy. You can include Forgetting Sarah Marshall among the successes.

FORGETTING SARAH MARSHALL (3 ) Directed by Nicholas Stoller • Starring Jason Segel, Kristen Bell and Mila Kunis • R, 112 min. •At the Century Cinemas Del Monte Center, Maya Cinemas, Northridge Cinemas.