LOS ANGELES — From Ernest Borgnine in "Marty" to Jon Favreau in "Swingers," Hollywood has long portrayed sensitive men humbled at the feet of cold-hearted women.

But never has a guy been put down quite like Jason Segel in "Forgetting Sarah Marshall." In his breakout role, Segel reveals his knack for a raw vulnerability that would be depressing if it wasn't so funny.

And "reveals" is the operative word.

In the opening scenes, Segel's character misinterprets the reason for his girlfriend's urgent visit. Instead of a roll in the hay _ and he has completely disrobed in preparation _ Sarah Marshall has come to dump him.

Utterly distraught, he doesn't cover up for Marshall (Kristen Bell) _ or for the camera. In several full frontal shots, Segel completely bares himself.

The R-rated gag is already the most-talked about scene in the film. It's culled from an experience the 28-year-old Segel _ who wrote "Sarah Marshall" _ had several years ago. He says it's presented "almost verbatim" in the movie.

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"This naked breakup commenced and, honest to God _ maybe this is part of the problem _ all I kept thinking was, `This is ... hilarious,'" Segel recalls.

In a recent interview on the set of "How I Met Your Mother," where he is a co-star, the 6-foot-4 Segel is much like his characters suggest he would be: good-natured and a little sheepish.

"He kind of has a gentle giant thing going on," says "Sarah Marshall" director Nicholas Stoller, who's also a close friend of Segel's. "His eyes naturally look hurt, but he's not actually a depressed guy. He's a very positive, happy guy."

A Los Angeles native, Segel was "noticed" when Paramount's president of casting happened to be in the audience of his high-school production of Edward Albee's "The Zoo Story," which Segel says he was putting on "for almost no reason at all."

After a few small film roles, Segel's career began in earnest when Judd Apatow cast him in "Freaks and Geeks," the revered high school comedy that was canceled in 2000 after one season. It has since established a fervent cult following, and was a foundational experience for Apatow, Segel and much of the young cast, which included Seth Rogen and James Franco.

As Nick Andopolis, Segel was both exceptionally earnest and terribly awkward _ trying to impress girls with his 29-piece drum set, for example. In Apatow's next TV show, the similarly short-lived "Undeclared" (2001-2002), Segel played a lovelorn long-distance boyfriend.

"It's always funny to watch Jason get beat up on and suffer," says Apatow, who produced "Sarah Marshall." "He's just fun to watch feel pain and that's always what made me laugh about him."

Says Segel: "Judd and I really collided on the idea that, for some reason, I'm able to remain likable while getting awfully close to the creepy line. It's one of my strange skills, so we've definitely cultivated that for ten years now."

After "Undeclared," Segel was out of work until Apatow's fortunes skyrocketed with 2005's "The 40 Year-Old Virgin."

On a Thursday soon after the film opened, the two went to a Laker game. Apatow informed him: "`Listen, I can get movies made now. Are you writing?'"

Segel told him about "Forgetting Sarah Marshall," sent him an outline the next day, and received contracts from Universal by Monday. Still shaking his head, Segel says, "It's ridiculous. It's nuts."

In the film, Segel's character attempts to get over Marshall by taking a trip to a resort in Hawaii, where, coincidentally, Marshall is staying with her new boyfriend, a British rocker played by Russell Brand.

Many of the supporting roles are filed by Apatow regulars _ Paul Rudd, Jonah Hill, Bill Hader _ but the new love interest, a hotel receptionist, is played by Mila Kunis ("That `70s Show").

It's received strong reviews and been heavily promoted by the studio, thanks largely to Apatow's track record. Besides "Virgin," he produced "Superbad" and directed "Knocked Up" _ in which Segel played Rogen's friend, the aggressive and cheesy seducer.

"My character in `Forgetting Sarah Marshall' couldn't be more different than my character in `Knocked Up,' but sadly, I think there's some of me in both," says Segel. "It really depends on how much I've had to drink."

Progressing from bit player to box-office comic star like Steve Carell ("Virgin") and Rogen ("Knocked Up," "Superbad") won't be easy. Segel has faith in the film, though, and besides, he's already swimming in new projects.

He's currently filming "I Love You, Man," co-starring Rudd; he's writing a script titled "Five-year Engagement" that Stoller will direct and Apatow will produce; and he's writing a script with Stoller for a new Muppet movie for Disney. (Segel counts Kermit, "the original Tom Hanks, the everyman," as a major inspiration.)

At any rate, Segel doesn't expect to run out of real-life material for his films.

"I'm filled with horribly awkward moments," he says. "It's probably why I don't sleep very well."