Spoiler alert: In Our Idiot Brother, the guy who’s the biggest moron among his family, his friends, and the whole of mankind ends up being the smartest of them all. Did I ruin it for you? Then you don’t have to waste your money on this promising but lifeless Sundance darling, which essentially takes Paul Rudd’s most irritating and unfunny character—Chuck, the stoner surfer from Forgetting Sarah Marshall—and settles in with him for 90 minutes. Dude!

Directed by Jesse Peretz (The Ex) and written by David Schisgall and Evgenia Peretz (Jeese’s sister), Our Idiot Brother is so much lower-key than you’d expect, you’ll actually wish for some of the wackiness its title implies. Not that the actors don’t try. Rudd, of course, simply goes around “whoa”-ing as Ned, a biodynamic farmer who gets thrown in prison for selling weed to a cop and then needs a place to stay when he gets out, his girlfriend (Kathryn Hahn) having left him, evicted him, and kept his dog. So he turns to his sisters. Natalie (Zooey Deschanel) is the one most on Ned’s wavelength, a bisexual stand-up comedian who lives in a veritable commune and is nervous about moving in with her girlfriend (Rashida Jones, in distractingly gigantic and hideous glasses to look butch). Writer Miranda (Elizabeth Banks) and stay-at-home mom Liz (Emily Mortimer), however, are the high-strung type As that this paint-by-numbers script requires, and you can see Banks and Mortimer (more the former than the straighter-laced latter) manically straining to wring laughs out of their “I can’t believe he…!” lines.

Regarding what they can’t believe Ned did—well, name it. He ruins Miranda’s professional and love life. He upsets the imagined harmony in Liz’s marriage by suggesting to his other sisters that her husband (Steve Coogan, playing a first-rate dick) is having an affair. He dares to play martial arts with their son, River (Matthew Mindler). (Wait, wouldn’t this hippie be even more against fighting than his sis?) And he also threatens to tank Natalie’s relationship. Mostly, Ned does these things by opening his big mouth. Like when he tells his parole officer that he got so stressed out one night he smoked a joint.

Hardly a minute of it feels believable. There is one sincere sequence: During a night of family charades in which the sisters roll their eyes and Ned uncharacteristically but justifiably goes off on them, he finally seems like a fully formed human being. Another detail is shockingly genuine: Liz, in glasses with no makeup and hair messily pulled back, looks like a real mom. You think, Wow, it’s refreshing that the film’s creators would allow an actress to appear that way. Alas, it turns out to have to do with a plot point about how un-“fuckable” she’s become.

Our Idiot Brother may have come off the quasi-indie circuit (it’s being distributed by the Weinstein Company), but its heart is full-fledged, no-risk Hollywood dramedy. Rudd’s next move should be to shave off the beard, cut the hair, and return to the Apatovian bromances from whence he so successfully came.