If the goal of "Observe and Report" is to show us the dark, transgressive side of Seth Rogen, then the movie is a bust. Rogen can no more creep us out than he could dazzle us with his knack for Elizabethan drama. It's not his fault that the first thing we perceive whenever he appears onscreen is the lovable shlubbiness that's made him a star; it does seem to be his fate here, however, to be unable to find his way out of that persona. And he's not helped by the movie's muddled conception. Whenever his character — Ronnie Barnhardt, mall cop — suddenly goes nasty (smacking a kid, insulting a blameless counter girl, heaping ethnic invective on an Indian mall merchant), it comes out of nowhere. We're eventually informed that Ronnie is bipolar, but that's just a narrative Post-it note: The movie has no interest in exploring an emotional disorder, and simply invoking one can't justify the script's lack of character motivation and its general disorganization.

Director Jody Hill wrote the screenplay himself. In scripting his last film, "The Foot Fist Way," he was assisted by its star, the gifted Danny McBride. "Foot Fist" also concerned a clod without a clue, but McBride's tickling, astringent borishness was enough to sell the character; no doctor's note was necessary. McBride makes a cameo appearance in "Observe and Report," playing a wild-eyed crack dealer, and his unhinged comic energy gives the movie a jolt of giddy pleasure.

Pleasure may be too square a thing to interest Hill, but he might have been more attentive to pacing and plausibility. The movie is a flat succession of incidents with no build. Ronnie longs to become a real cop — to trade in the Taser and Mace he carries as a security guard and begin packing a gun. When a fat flasher starts terrorizing women at the mall (we get to contemplate the man's jiggling junk at length), Ronnie sees capturing this nutter as his ticket to the big time. The mall calls in actual police, though, led by Detective Harrison (Ray Liotta, looking waxen), and Ronnie, in a fit of territoriality, flips out. But he flips out at everything, sometimes for no discernible reason. (A monotonous volley of unadorned castigation — "F--- you!" "No, f--- you!" — between Ronnie and the Indian guy [Aziz Ansari] is inexplicable, and sputters out before it actually ends.) But no matter how ballistic Ronnie goes, there are never any consequences: After single-handedly beating down an improbable number of cops in a big bloody fight, he simply moves on — not to major jail time, just to the next scene.

The movie is worth watching for some of the inventive performances orbiting Rogen's meandering hostility. The wildest — and most unexpected — is by Michael Peña (still memorable as a half-buried cop in "World Trade Center"). He plays a character named Dennis — one of the subordinate security guards on Ronnie's patrol team — as a lisping, drug-fogged hipster who thinks Ronnie should ditch his dream of becoming a police officer and go in an entirely different direction. There's clearly something twisted about Dennis, but we only sense it at first (until a big reveal, which piddles away), so the character engages us. As does the delectable Anna Faris, who plays the cosmetics salesgirl Brandi — a trashy variation on the adorable naïf she created in "The House Bunny." Brandi is a tramp and (typically, in this picture) nothing else. We see her careening home at full whoop one night in a car full of bellowing male companions, and we've got her number. I guess her airhead sluttiness is intended as a rationale for a later scene in which Brandi — whacked on tequila and a handful of clonazepam tablets she's eagerly accepted from Ronnie (they're his meds) — has nod-out sex with him, her head lolling on a pillow puddled with vomit. This is really gross and really funny, and I didn't think it qualified as a date-rape joke (when Ronnie pauses in uncertainty, Brandi snaps to and demands that he continue). I have a feeling there are people who might, though.

Celia Weston also has some fine, woozy moments as Ronnie's falling-down-drunkard mom, who loves her idiot son as much as anyone could. ("You may not be the smartest person in the world, but you're handsome ... from certain angles.") But Hill, in constant search of edginess, has Weston mouthing lines about boffing Ronnie's friends when he was in high school, and about a recent bender during which "I soiled my pants," and we want to tiptoe away — and take her with us.

In interviews, Rogen has said that he and Hill wanted to make a comedic version of "Taxi Driver" — as if that were a good idea. The Scorsese film has lashings of savage humor that are leagues beyond anything contemplated here. And the sweet, doughy Rogen, even with his faultless comic timing, is wrong for a jokey Travis Bickle. (It's hard to imagine who'd be right.) Of course he'll branch out creatively in the future — he's only 26, why not? But Hill's glib nihilism is beneath him. Right now, he's too good at what he does so well to be doing this.

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