Anyone with more than a passing interest in Judd Apatow's career will note how there's a curious call-back to one of Apatow's earlier works in this most recent of his productions, with the credits for Step Brothers in the exact same scrawled, stretched-out font as his comedy Freaks and Geeks. Freaks and Geeks, though, featured teens who often spoke and acted like adults; Step Brothers features adults who constantly speak and act like children.

The credit-font's evocation of an earlier Apatow work is an omen for the rest of Step Brothers, in fact, with Will Ferrell and John C. Reilly recycling and amplifying their rivalry from Talladega Nights: The Ballad of Ricky Bobby (also directed by Step Brothers helmer Adam McKay) but without that film's plot structure, surreal wit or inspired mockery (and celebration) of NASCAR culture; instead, Step Brothers seems constructed -- or, rather, contrived -- solely to create a circumstance where Ferrell and Reilly can act like idiot man-children and riff to their great amusement. That, however, is not the same thing as riffing to the amusement of the audience. ...

Step Brothers starts from a tissue-thin premise, as Dr. Robert Doback (Richard Jenkins) meets, and falls for, Nancy Huff (Mary Steenburgen). The two of them are professional, bright people ... who have overgrown, underemployed sons living at home with them. Robert's burden is the loud, overbearing Dale (Reilly); Nancy's is the overbearing, loud Brennan (Ferrell). As Nancy and Brennan move in with Robert and Dale, you may ask yourself why it is the boys are both still bound to their parents, and why ultimatums or stratagems to blast the boys free from the home haven't been tried before; the script provides no answer to that simple question, as it's too busy rushing to get to the scene where Ferrell rubs his reproductive equipment on Reilly's beloved drum kit, or the scene where a grade school girl in pigtails barks out "Shut your mouth, ese!" or the scene where Ferrell and Reilly, both sleepwalking, grunt gibberish while trashing the kitchen.

That last moment, in fact, is one of many that hint at how a little more structure and a little less free reign might have made Step Brothers funnier; the idea that Brennan and Dale have matching deep-seated neurological disorders might explain a lot. Anything explaining what made Brennan and Dale the way they are, in fact, would be to the betterment of the film. But, instead, it's implied that Ferrell and Reilly's characters are the way they are because they're played by Ferrell and Reilly.

Brennan and Dale feud, fuss and fight for a while, until they realize they both love the same things -- karate, velociraptors, John Stamos -- and have a common enemy, Brennan's younger brother Derek (Adam Scott). Derek is a bully, a thug and -- most damningly -- a Dane Cook fan, and when he offers to sell Robert's house for above-market value, Dale and Brennan fight back to keep from losing their home. In Talledega Nights, Ferrell and Reilly faced down Sacha Baron Cohen -- a worthy comedic adversary. Scott may be a high-fiving hateful go-getter moron, but he's not enough of a presence, on the screen or on the page, to engage us in his struggle against Ferrell and Reilly.

There are, perhaps, three laughs in Step Brothers -- a funny shovel-fight, a joke about a cover band that only does "'80's Billy Joel," called Uptown Girl, and a fantasy sequence where Ferrell's psychiatrist sees him in a whole new light while he's singing an operatic aria. That's it, really. The rest is just mean, sprawling, self-indulgent flailing, as if someone warmed up the comedy machine at the Apatow factory and forgot to sprinkle the heart and the teaspoonful of structure when they tipped in the three bags full of raunch, randomness and recklessness.

Jenkins and Steenburgen are actually good, but their performances are so grounded and real and natural that they just make Ferrell and Reilly seem all the more overblown and phony. Talladega Nights (and, for that matter, the lesser Anchorman) took place in a world that was insane, so the antics and madness of the characters blended into a bright, blurry background of comedy and lunacy; in Step Brothers, with Dale and Brennan in the real world, we're annoyed by the characters, not amused by them.

Early in Step Brothers, Dr. Doback tells his son "Dale, I think that it's time we both made a few changes. " Would that screenwriters McKay and Farrell had taken that advice to heart; instead, Step Brothers offers more of the same from Ferrell -- the idiot, undeserved over-confidence he's brought to a dozen films -- and more of the same from Reilly -- the fuzzy, dimwitted-but-warmhearted loutishness he's played a little too often -- as well.

A better movie might have explored what the parents got out of their long-suffering stewardship of their sons, if it made them feel necessary or gave them a chance to concentrate on fixing someone else's life instead of their own; alternately, writing Dale and Brennan as something deeper than braying idiots might have helped the film feel less forced. But there's nothing here to match the foul-mouthed, warm-hearted male bonding in The 40-Year-Old Virgin or the phony-brave mistaken melonhead machismo in Superbad or the surreal satire of Talladega Nights; instead, all we get is scuffles and shouting, pranks and poo jokes, with a mealy-mouthed message about being true to yourself tacked on at the end like a shiny bow wrapped around a bag of trash.

Step Brothers may be a story of sibling rivalry and extended adolescence, but trust me, it works far better as a cautionary tale about the damage incestuous inbreeding can do to a film if it's not just unchecked but in fact encouraged.