Not good, but inoffensive, "Our Idiot Brother" exists in a kind of Dead Zone of entertainment. It's mediocre in a passive, energy-sapping way midway between humdrum and ho-hum.

Paul Rudd, likable in Judd Apatow films but insipid here, stars as Ned, an affable pothead. We meet him staffing a vegetable stand at a small-town farmers market, and we quickly see that Ned is sort of a vegetable himself, wide-eyed but unseeing. The character is saddled with enough innocence to make a Clydesdale buckle. He's established as a sweet, goodhearted simpleton by selling pot to a uniformed police officer.

When the poor sap emerges from jail on probation, his abrasive hippie farmer girlfriend (Kathryn Hahn) sends him packing, having found a new stoner to boss around during Ned's time behind bars. Too bad; Hahn's cameo as a dreadlocked, tie-dyed, pacifist tyrant is sublime. The brief wrangles between this despotic Earth mother and Ned the passive, drooping flower child are the movie's most idiosyncratically funny moments.

Ned takes his loving, goofy, kooky act to New York City, where he hopes to crash with his sisters Liz, Miranda and Natalie (Emily Mortimer, Elizabeth Banks and Zooey Deschanel), who regard him as a troublesome mascot. His arrival triggers trivial traumas and flaccid comedy skits. Each actress plays a specific New York type; the problem is that they remain stereotypes, never coming into focus as authentic individuals.

Mortimer is a striving upscale Brooklyn mom married to an insufferable documentary filmmaker (Steve Coogan, displaying none of his usual I-dare-you-to-hate-me charm). Banks is a Vanity Fair writer fretting over her first big assignment, a profile of a scandal-tainted English princess. Deschanel is a no-talent standup comedian with promiscuity issues, dating a lawyer named Cindy (Rashida Jones) but undecided about which side of the bisexual spectrum she really belongs on.

Like a holy fool in cargo shorts and flip-flops, hapless Ned bumbles through each woman's life just long enough to help her achieve a breakthrough. Liz realizes that she's facing bigger issues than getting her kids into exclusive private schools. Miranda reorders her work and life priorities. Liz gets her act together.

This is not a story but a jumble of vignettes. The script tries to link the episodes like so many points in a connect-the-dots drawing. But no picture appears. The points provide no more design than random specks on a blank wall. The dialogue is aimless chitchat, sometimes amusing but directionless. The sequences intended to be heartwarming are merely tepid.

The story depends on our concern for guileless Ned and our affection for Rudd. I felt little in either category. Ned meets every setback with a shrug. This flavorless film deserves the same.