Even if "The Change-Up" cannot attest to being the best in a long line of time-honored body-swapping comedies, it certainly has the market cornered on filthiness. Directed by David Dobkin (2007's "Fred Claus"), the film barrels straight through good taste into a realm of un-PC fearlessness that somehow narrowly avoids cruelty. For all of its gross-out humor—some of it works, some of it doesn't—the movie listens to, respects, and cares about its characters. Scattershot though the narrative is, at its core is a certain disarming sweetness. For screenwriters Jon Lucas and Scott Moore, previously responsible for 2009's mean-spirited, derogatory "The Hangover," this is definitely a step up.

Married father-of-three Dave Lockwood (Jason Bateman) is a straight-laced, workaholic lawyer thisclose to making partner at the firm he works at. In his drive to be successful and make money, however, his relationship with wife Jamie (Leslie Mann) has gone on the back burner and begun to suffer as a result. Mitch Planko (Ryan Reynolds) has been Dave's friend since the third grade, but his life has taken a, shall we say, different path. An actor more often than not out of a job, the perpetually single Mitch spends his days getting high, doing what he wants to do, and bedding as many women as he can. In a moment of letting off steam, both guys wish they had the other's life, verbalizing just as much as they simultaneously urinate into a mysterious park fountain. Overnight, in an instant, Dave and Mitch switch places and bodies. With the fountain conveniently out of commission as the city prepares to relocate it, they have no choice but to pose as each other for the week. The loud, uncouth Mitch (as Dave) suddenly has a family and a profession he knows nothing about, while Dave (as Mitch) now has all the free time he's dreamed about (once, that is, he deals with shooting a lorno—light porno—Mitch has been cast in). As Dave starts to spend more and more time with knockout co-worker Sabrina (Olivia Wilde), he moves closer to fulfilling one of his fantasies even as he recognizes the reality—a wife and children he dearly loves—is so much better. Mitch, meanwhile, begins to realize how much growing up he still needs to do as he watches his friend's marriage edge closer to crumbling.

The distasteful opening scene in "The Change-Up" is less than reassuring, revolving around an early-morning diaper change that culminates in a baby's flinching bare buttocks and a spray of poop showering Dave's face, and then inside his mouth. There is no point to any of this other than to kick things off with a literal gag straight away, and it's as desperate as it sounds. Fortunately, the film brightens considerably as the plot gets underway and the viewer gets to know the two starkly different protagonists. From 1988's "Vice Versa" and "Big" to 2002's "The Hot Chick" to 2003's "Freaky Friday" to 2004's "13 Going on 30," body-swapping is a go-to cinematic formula that more often than not works because of the prime comic material that naturally permeates from such a premise. As long as the script and actors are up to snuff, it's fun to see a character who is not really who others think they are flounder as they attempt to keep up appearances in "fish-out-of-water" scenarios. Physically, the two thirty-something guys changing bodies aren't as different as, for example, a child and parent, but their personalities are so night and day that this makes up for it.

Mitch has no filter for what comes out of his mouth, and what comes out is usually pretty unspeakable as he contends with Dave's important meetings at work and interacting with his friend's wife and kids. Thinking nothing of spouting off religious and ethnic slurs and advising six-year-old daughter Kara (Sydney Rouviere) to solve the problems she's having with a mean girl in her ballet class by turning to violence—"if someone crosses you, put their family in the fucking morgue," he goes on to tell her—Mitch is a wrong-headed mess made hilariously acidic in that it's now all coming out of Dave's mouth. In a role that asks him to play against-type, Jason Bateman (2011's "Horrible Bosses") lets looser than viewers may have ever seen him. Even when, as Mitch, he's doing some awful and disrespectful things, the actor still keeps him oddly likable. Bateman plays it all straight, but he's more than in on the joke. As Mitch (and, later, Dave as Mitch), Ryan Reynolds (2011's "Green Lantern") is believable as a jack-ass and as the good guy learning about himself as he takes some time to breathe and relax without the stresses of work. The set-piece where Dave reports to the set of Mitch's movie only to learn he's to perform a sex scene in a Skinemax flick with a much-older woman and another man is deliciously uncomfortable and nervously amusing before ending on a gay-panic punchline that could have been done without. More impacting, though, is the film's simple but affecting snapshot of a hard-working guy taking time for himself and living it up for a spell before he returns to the life he knows he's meant to have.

As humor-driven as it can be, the film's emotional undercurrent gives the story a welcome anchoring levity. The rocky marital relationship between Dave and Jamie is raw and sobering in its truthfulness, and the way Leslie Mann (2009's "Funny People") plays it is pitch-perfect. Mann is a funny performer, but also underrated as a dramatic actor; faced with doing both here, she paints an aching three-dimensional picture of a woman who keeps hoping that her husband's career successes will finally fill the hole missing from his childhood and bring him back to her. Olivia Wilde makes the most of her part, too, as Sabrina, much looser and more impressionable here than in the recent "Cowboys & Aliens." Sabrina's role could have been thankless—that of the dream girl at work that Dave finally gets a shot with in Mitch's body—but Sabrina is written as free-spirited but intelligent, level-headed and understanding. When, over dinner, Mitch expresses his hope that she wasn't offended by the sexually explicit remarks Dave made toward her in the office, Sabrina has a great comeback line: "I like being offended, but usually after work."

"The Change-Up" dares to go to certain places mainstream studio pictures rarely have the courage to approach. Some of it is queasy—Dave must fend off Mitch's nine-months-pregnant predatory booty call Tatiana (Mircea Monroe)—and other parts are of the "am-I-really-seeing-this?" variety—an instance involving two babies and a kitchen full of knives, cleavers, blenders and electrical outlets comes to mind—but in between the raunchy outrageousness is, believe it or not, a more thoughtful soul. Dave's and Mitch's respective stories are uneven at times as the film tends to concentrate its focus on one of them or the other rather than both alternately, but this temporary editorial lag is not enough to lose sight of the earnest empathy afforded Dave and the lower-key catharsis Mitch experiences. Indeed, it's a requirement that body-swapping movies end with the character(s) learning to appreciate what they have (otherwise what's the point?), so the story's trajectory is never in question. The key is how well it's pulled off. "The Change-Up" is blue and bawdy as all get-out, but it turns out this is just a ruse for the heart hiding underneath. Still, perhaps director David Dobkin ought to leave the fecal matter on the cutting room floor next time.