Opening with an infant taking a crap directly in lawyer Dave's (Jason Bateman) mouth, The Change-Up begins at the absolute bottom so it can only ascend thereafter, a calculated strategy that nonetheless doesn't allow this middling R-rated effort to transcend its groan-worthy Freaky Friday setup. Wielding nudity and profanity like they were comedic be-all end-alls, Wedding Crashers director David Dobkin and The Hangover's scribes Jon Lucas and Scott Moore do their damndest to adult-ify their premise, in which straight-and-narrow Dave and his pothead lothario slacker friend Mitch (Ryan Reynolds) both wish to be the other while peeing in a public fountain, and wake up the next morning to find that said desire has come true.
Such extremeness is perhaps the only way to enliven this otherwise stale scenario, and to be sure, the occasional out-there bit does land squarely, as with a scene in which Mitch (in Dave's body), trying to feed twin babies, places them on a kitchen counter and one promptly sticks its tongue in an electric socket. Yet as is so often the case with the frat-boy genre to which this film panders, so many gags feel like desperate, self-conscious attempts to be outrageous (for example, Mitch's sexually ravenous booty call turns out to be nine months pregnant!) that the effect of its abundant cursing and boob shots is more depressing than delirious. Additionally, the over-the-top ribaldry of Dave and Mitch floundering in each other's lives is itself somewhat disingenuous, functioning not as a means of parodying happily-ever-after body-swapping movies, but as a way of simply distracting attention away from the fact that it's actually one of those fairy-tale films. Dave is forced to insert his finger into an aging fake-breasted actress's butt while performing in Mitch's "lorno" (light porno), and Mitch has to cope with Dave's wife, Jamie (Leslie Mann), having diarrhea in the bathroom.
However, for all that faux-craziness (shot, as is Dobkin's habit, with uninviting flatness), The Change-Up is really about Dave learning to enjoy life and prize family over career, and Mitch understanding that he has to grow up and reconnect with his father (Alan Arkin). That formula is so squishy, tired, and front-and-center that much of the film's insanity comes off as window dressing, even though the sheer number of jokes thrown at the screen means that the proceedings often prove just stupid enough to be mildly amusing, such as a hoary subplot about Mitch (as Dave) teaching his daughter to stand up to a ballet-class bully by fighting back because "violence is cool."
In keeping with guys-guy comedies' general disdain for women, The Change-Up posits Jamie as another one of Mann's whiny, intimidating hard-asses who's constantly frustrated by her husband (and who's also compelled to twice go topless for no appreciable humorous reason), and as one of Dave's coworkers, Olivia Wilde is asked to be merely an ideal of sports and tattoo-loving hotness. Yet it's ultimately hard to completely slam the story as reductively sexist when its lead male characters are similarly two-dimensional clichés, and unequal ones at that, since Mitch's struggles to be a responsible parent, spouse, and lawyer are far more arduous than Dave's efforts to be cool, laidback, and horny.
Both Reynolds and Bateman seem somewhat unshackled by this subpar material, with the former liberated from being just a sarcastic hunk in numerous situations that call for flustered exasperation, and the latter—more assured and lively than he was in Horrible Bosses—radiating uninhibited loopiness in scenarios that require him to behave in a profanely idiotic, limbs-flailing, "dude, whatever" manner. They're both so likeably unaffected that they almost salvage The Change-Up on wild-abandon charisma alone, though typical of a wannabe Judd Apatow effort, any early zaniness is subsumed under unwanted climactic schmaltz that, ultimately, is as rank as the opening's pie-hole pooping.