Entertainment

TONGUE-IN-GEEK

I have to admit that in at least one way, “Forgetting Sarah Marshall” represents an advance in the geek-comedy universe of Judd Apatow.

Instead of the usual flabby guys running around in their underwear, writer-star Jason Segel ups the ante by showing off the full monty in several scenes.

This film is so funny it may be beside the point to complain that, as in many Apatow productions, the writing and direction are still in something of a state of arrested development.

Segel’s Peter drops his towel – and refuses to cover up his, uh, peter as his girlfriend Sarah (Kristen Bell) proceeds to break up with him.

In a role reversal of your usual romantic comedy, Peter – a composer of hackneyed musical themes for the “CSI” knockoff Sarah stars in – cries a lot. And his misery only gets worse when he books an ill-timed Hawaiian getaway.

Sarah and her new boyfriend, a British rocker named Aldous (Russell Brand), are athletically cavorting in the room next door.

That leaves Peter to drown his sorrows at the bar with a confused newlywed (Jack McBrayer) – and to nearly literally drown under the dubious tutelage of a stoner surfboard instructor (a very funny Paul Rudd).

It’s pretty obvious that Peter is eventually going to notice Sarah (like so many characters in the phallocentric Apatow-iverse) is an emasculating bitch and that he really should be interested in that nice Rachel (Mila Kunis) at the reservations desk.

Somehow this simple story, which ought to take no more than 90 minutes, clocks in at nearly two hours.

Debuting director Nicholas Stoller, another of Apatow’s TV cronies, has to work in cameos by other members of the stock company, including Jonah Hill and Jason Bateman. And this being a Universal Pictures release, there are many shameless production placements, especially on behalf of sister-company NBC.

Segel, perhaps best known for his role on “How I Met Your Mother,” has a flair for physical comedy and there is some very funny stuff in his supposedly autobiographical script, even if it seems like a first draft.

Most of the best lines go to Brand, a veteran British comedian who steals the flick and turns out to be its most appealing character.

Even Stoller’s flaccid direction – abetted by haphazard editing – can’t seriously damage the charming final sequence, Peter’s puppet-musical version of “Dracula.”

Unlike its Apatovian predecessors – “The 40 Year Old Virgin” and “Knocked Up” – “Forgetting Sarah Marshall” will probably be remembered primarily for its star’s nude scenes.

lou.lumenick@nypost.com