It’s a joy to watch a film directed by Kevin Smith when he’s at the top of his game. Like a geek-ified David Mamet, Smith can drop unique characters into scripts laced with pop-culture references and a quirky sense of humor, all conveyed through a remarkably varied use of profanity.

When Smith’s approach works, we get films that are vulgar but honest. Movies like “Clerks,” “Chasing Amy” and “Dogma” manage to be consistently funny and occasionally insightful.

But what happens when Kevin Smith’s approach doesn’t work?

Well, that’s when we get a film like “Cop Out.”

“Cop Out” stars Bruce Willis and Tracy Morgan as a pair of veteran, yet spectacularly inept, New York City police detectives. The plot revolves around a valuable baseball card that, once stolen, turns out to be an equally valuable plot-contrivance as attempts to reclaim the card lead Jimmy and Paul into a showdown with the city’s most powerful drug-lord.

Willis seems to be on the acting-equivalent of autopilot for most of the film, coasting through a role that’s marked by its lack of personality. But if Willis’ character is short on charisma, Morgan’s is plagued with it, as the “30 Rock” actor takes his usual approach to reciting lines: as loudly as possible. It’s his delivery style that can become abrasive over the course of a four-minute “Saturday Night Live” skit, and in “Cop Out,” we’re stuck with it for two hours.

But the main problem with “Cop Out” isn’t the acting. It’s the script. Although director Kevin Smith didn’t actually write the screenplay, (marking the first time in Smith’s career that he’s directed someone else’s work) the dialogue certainly caters to his reputation for vulgarity.

However, the lewd comedy found in “Cop Out” feels unnatural — like it’s been transplanted for appearance’s sake. One might even say “Cop Out” is an appropriate title for the film as Smith seems to be grudgingly going through the motions, providing his audience with plenty of his trademark crude humor and pop-culture shout-outs while avoiding any true notion of directorial sincerity.

Still, it must be said that there are times when “Cop Out” is slightly enjoyable. If you’re willing to take the film as a loose parody of an ‘80s buddy-cop movies, then it’s even occasionally funny.

Boasting a soundtrack reminiscent of the one found in “Beverly Hills Cop,” “Cop Out” plays off formulaic 1980s cop-flicks like “48 Hrs.” and “Running Scared,” films that invariably depend upon racial stereotypes and tout a brand of movie-logic that allows for police officers to shoot up an entire city block and get off with only a mild reprimand and a brief suspension.

The movie’s most tolerable moments come from this spirit of parody. Supporting actors Kevin Pollack and Adam Brody are even genuinely funny at times, playing a pair of straight-laced detectives whose professional relationship ever so slightly hints at the homoeroticism that underwrites machismo-fueled buddy-cop flicks like “Lethal Weapon” and “Tango & Cash.”

However, Kevin Smith is no Mel Brooks, and he’s unable to balance lowbrow humor with subtle satire. As a result, the parody found in “Cop Out” is vague and uneven, often vanishing upon the arrival of the film’s next joke concerning bodily-functions.

So “Cop Out” manages to be both a Kevin Smith film without the expected attitude and a genre-parody without the required edge.

At least it’s versatile in its failure.

Rating: 1 ½ out of four

Bottom line: “Cop Out” is a crude mash-up, attempting both genre parody and director fetish. It fails to be successful at either.