"Inappropriate," today's foremost throat-clearing adjective, is the appropriate response to The D Train. This squirm-till-you-snicker comedy is about two immature males confronted with sexual possibilities they can't handle. One of the guys is 14; the other is his father.

Dad is Dan Landsman (Jack Black), who lives in Pittsburgh with his wife (Kathryn Hahn) and two kids. He does something for some sort of consulting firm, but his passion is being the self-appointed chairman of his high school 20th reunion committee. Dan was a loser two decades ago and still is, even among a bunch of reunion organizers who mostly appear as uncool as he is. (One of them is played by Black's pal, writer-actor-director Mike White, who specializes in the gauche and gawky.)

One night while watching TV, Dan glimpses salvation: a suntan lotion ad that stars a former classmate, Oliver Lawless (James Marsden). Dan decides to boost his status by recruiting Oliver to attend the reunion. Somehow it doesn't occur to Dan that a demi-star's arrival at the party might push the class's lesser lights further into shadow.

There are worse things than being ignored, though, and Dan is about to experience several of them. First, he betrays his boss, Bill (Jeffrey Tambor), by pretending to have found a hot prospect in Los Angeles. Bill is so excited that he insists on going along. This leads to one of the several mortifications Dan could avoid if he'd just figure out the right way to say, "no."

Dan arrives in somebody's musty notion of hip L.A., where he meets Oliver. The handsome actor turns out to be just as much of wannabe as Dan. He's not connected and barely working, although he doesn't seem to be too strapped to afford cocaine. He's also bisexual, which is where Dan becomes really uncomfortable.

Viewers are meant to share that discomfort. But the plot — like that of the movie's thematic precursor, Get Him To The Greek — is less transgressive than arbitrary.

Upon returning to Pittsburgh, Dan is too fixated on his own issues to help his son, Zach (Russell Posner). The barely teenage kid has a new, slightly older girlfriend who wants his sexual initiation to be a threesome. You might think that both parents would have an opinion about this, but the only person who offers any advice is Oliver. And his counsel is purely pragmatic.

Writer-directors Jarrad Paul and Andrew Mogel set up Dan and Zach's sexual crises sloppily, so it's unsurprising when the payoffs prove equally careless. The filmmakers proceed as if they're making a conventional high-school comedy, papering over the holes in the script with pop songs. (Dan's lameness is underlined by such attempts at hip-hop parlance as picking "D Train" for a nickname, yet the music is nearly all mainstream pop-rock. And most of it is from the 1980s, even though Dan and Oliver are class of '94.)

Black's career has sputtered recently, and Marsden seldom gets a role worthy of his talents. Perhaps that's why the duo decided to emulate the hunk/schlub dynamic that James Franco and Seth Rogen have ridden all the way to North Korea. The D Train won't inspire so excited a response. Just a few "ughs" and shrugs before it rumbles out of theaters next week.

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