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“Step Brothers” is aimed at the lowest common denominator.

The title is “Step Brothers.” (You know, because there are two of them.) But Will Ferrell and John C. Reilly are essentially playing the same person, which is the movie’s fundamental, irreparable flaw.

As 40-year-olds who’ve never left home and are forced to share a bedroom when their parents get married, Ferrell and Reilly are stuck in the same state of arrested development. There’s no odd-couple tension, no witty banter, just a prolonged, painfully unfunny game of one-upmanship in which each actor is trying to outdo the other in one-note obnoxiousness. You wouldn’t want to spend two hours with one of these guys, much less both.

The humorously awkward chemistry these actors shared as teammates in “Talladega Nights: The Ballad of Ricky Bobby” is long gone, because the script makes no room for it. And that’s strange, because Ferrell co-wrote the screenplay with his old friend, director Adam McKay, with whom he collaborated on the NASCAR comedy.

Watching “Step Brothers,” though, it doesn’t take long to realize that their creative process consisted of sitting around, cracking each other up with adolescent gags, and then writing it all down. Whether the rest of the world will be doubled over with laughter seems irrelevant — and that insularity is ultimately alienating.

Many of the jokes are of the broad, physical variety and seemingly aimed at the lowest common denominator. It’s not that any of this stuff is offensive, it’s just hackneyed and flat.