From the poster, you might think Our Idiot Brother has all the elements for a great comedy -- Paul Rudd starring as a sweet, stoned doofus, opposite a cast of hilarious heavyweights like Elizabeth Banks, Emily Mortimer, Steve Coogan, Zooey Deschanel, Rashida Jones and Adam Scott.

But something went wrong along the way -- while the film does offer its share of zingy one-liners and entertaining character moments, the final result is a movie that can't decide if it wants to be snarkily sweet or mean and misanthropic.

And it's the female characters, for the most part, that wind up being the object of the movie's venom.

Rudd's Ned is a holy idiot, floating through life on a cloud of naivete and pot smoke. His relatively carefree existence gets upended when he sells weed to a uniformed police officer -- the movie isn't called Our Idiot Brother for nothing -- and when he gets out of jail, Ned's girlfriend Janet (Kathryn Hahn) has kicked him off of the upstate New York organic farm where he's been living with her and, even more troubling to Ned, announces that she's keeping Ned's beloved dog Willie Nelson.

Ned tries moving back in with his boozy mom (Shirley Knight) on Long Island, but he eventually heads to Manhattan, where he crashes with each of his sisters, with disastrous results.

While staying with supermom Liz (Mortimer), Ned helps out on a documentary directed by her husband Dylan (Coogan) and realizes that Dylan's having an affair; while hanging out with Vanity Fair reporter Miranda (Banks), he gets an aristocratic interview subject to open up about a past scandal, but then refuses to stand by the story when the ruthlessly ambitious Miranda tries to publish it; later, he blurts out the fact that untalented comedian Natalie (Deschanel) is pregnant, despite the fact that she's supposed to be in a monogamous relationship with lawyer Cindy (Jones, as the least convincing butch lesbian in the history of cinema).

So basically, Ned may be a twit, but the real problem is that he's so innocent, and his big mouth gets his sisters into trouble because he's shattering the lies that they've all created about themselves. (Liz should let her son take karate, and Miranda shouldn't try to work her way up the ladder on someone else's misery, and blah blah blah already.)

And while there's certainly a way to spin a modern Candide about a rube who disrupts the life of city folks and their duplicitous ways, Our Idiot Brother gives us a troika of irritating female characters who need their bumpkin brother to show up to fix their lives for them.

Toss in the shrewish and nasty Janet, and you've got a bubbling cauldron of misogyny -- in a movie that's, incidentally, co-written by a woman.

(Evgenia Peretz, sister of the film's director, seems to be setting out to slander both her gender and her day-job employer, Vanity Fair, since it paints the magazine as shallow and dirt-hungry.)

Still, the cast does what it can to keep things lively. From the misguided pot sale onward -- including a memorable moment in which Ned counts out a giant wad of cash on a crowded NYC subway -- Rudd takes a character who could have been unbelievably dopey and makes him a lovable lamb set loose among the wolves.

Banks and Scott generate sexy, bristly chemistry as two people who don't want to cop to their mutual attraction, and Coogan adds to his gallery of hilarious blowhards.

Up-and-comer T.J. Miller makes an impression as Billy, Janet's new boyfriend, the one person in the movie -- perhaps on Earth -- who's on Ned's wobbly wavelength. He and Rudd have such great comic rapport that director Jesse Peretz tacked on a new ending after the film's Sundance premiere to make it clear that Ned and Billy belong together but, like, in a totally bro way.

So it's odd, then, that a movie that had the potential to be such a humanist comedy treats so many of its human beings so poorly. Why such contempt for most of the female characters?

Couldn't Ned have had a brother whose life was also a mess? It's the stench of misogyny that makes this indie comedy go so very sour.