AUSTIN -- Seth Rogen tests the limits of his lovable-lug persona in "Observe and Report," playing a character who is at best wildly delusional and at worst a stalker in need of professional care.

Barring a Terry Zwigoff return to "Bad Santa" territory, it's hard to imagine a filmmaker embracing this dubious hero to the extent writer-director Jody Hill does. The result gets plenty of laughs but will leave an odd aftertaste that could make "Observe" less successful than Rogen's less ambiguous outings.

Rogen plays Ronnie Barnhardt, a mall cop -- make that supervisor of mall security -- in search of any occasion to validate the odd feelings of importance he shares with the loyal half-wits on his staff. The undercurrent of wry self-awareness that has endeared Rogen to viewers in the past evaporates here, leaving a manchild with enough body mass to do serious damage and with an easily wounded ego.

First in line to dish up ego bruises is Brandi (Anna Faris, relishing her character's snootiness), a makeup counter employee who openly disdains Ronnie until a brush with the mall flasher throws her into disarray. Audiences expecting sensitive treatment of sexual assault should look elsewhere. Rejecting the businesslike attitude of the police detective assigned to investigate (a perfectly cast Ray Liotta), Ronnie encourages Brandi to believe her life is in danger and persuades her to go out with him.

Having a pervert on the loose not only jump-starts Ronnie's love life but affords him a reason to try out for a job on the actual police force. Although the screenplay gets some laughs out of this quixotic effort, the sequence also is where dissonance sets in for good: As a bystander notes after seeing Ronnie's dream crushed, what promised to be funny actually is pretty sad.

Partly but not completely thanks to Rogen's committed performance, "Observe" manages the funny-pathetic arc of its story line vastly better than Hill's debut film (and the breakthrough of Danny McBride, who appears briefly here) "The Foot Fist Way." It stays on the rails even when Ronnie goes off them completely and manages to get in a climactic chase sequence that crowds will be telling friends about the next day.

One thing this film does draw from Hill's earlier one is an impressively obscure soundtrack that might start with the Band but immediately segues to groups like Pyramid, whose musical vigor far exceeds their songwriting gifts. It's hard to imagine a more appropriate accompaniment for a rent-a-cop who thinks he's a vigilante hero.