The ghost of John Hughes hovers over “Identity Thief,” and must be bemoaning how the winning combination of heart and humor he brought to “Planes, Trains & Automobiles” has itself been pilfered and perverted into the dismal concoction served up by director Seth Gordon.

The supposedly hilarious premise is that the life of Sandy Patterson (Jason Bateman), a account executive at a Denver firm, is turned upside down when he stupidly gives out over the phone the personal information that allows a conniving woman named Diana (Melissa McCarthy) calling from Florida to print up phony credit cards in his name and use them to destroy his finances. Picked up on warrant by a Denver detective (Morris Chestnut) over trouble the woman’s gotten into at a Florida bar, Sandy quickly convinces the cop that his identity’s been ripped off, but learns that the only way he can fix the situation quickly is to go down to the Sunshine State and bring the actual malefactor back to Colorado himself.

So Sandy’s off to Florida, where after some nasty knockabout slapstick he persuades the crook, a vulgar loud-mouth, to drive to Denver with him, promising her he won’t press charges if only she’ll clear him and save his job—and his happy married life with an adoring wife (Amanda Peet) and two darling daughters. Unfortunately, Diana’s in trouble both with the law and with an imprisoned mob boss (Jonathan Banks), which results in the pursuit of the unlikely pair by both a red-neck skip-tracker (Robert Patrick) and a couple of hit-persons (Tip “T.I.” Harris and Genesis Rodriguez).

Of course the cross-country trip is not without incident. There are numerous comically violent encounters with their pursuers—all of them tonally off-kilter and vaguely unpleasant. But since you can’t fill a feature with those alone, the script simply tosses in digressions to fill up space—a walk in the woods that leads to an encounter with a snake (again, so ineptly done that it’s more repulsive than funny), a sex scene between Diana and a horny cowboy-type, played by Eric Stonestreet, at a crummy motel (more gross than anything else). There are car chases and car wrecks, as well as scads of rough language designed to be naughtily amusing and, of course, the obligatory projectile-vomiting sequence (which at least occurs early on, so we don’t have to wait for it too long).

And needless to say, an important plot element is the gradual bonding that occurs between Sandy and Diana, which leads to them to be self-sacrificing, supportive buddies by the close. That necessarily involves inventing a schmaltzy sob back-story for the woman that ultimately wins Sandy’s sympathy, and supposedly ours. Certainly by the final scene Sandy’s adorable kids are treating her like Aunt Diana, whatever her real name might be.

In this case, though, that’s a hard row to hoe, because in McCarthy’s hands Diana is such an abrasive, obnoxious person, an attitude that persists despite occasional asides meant to show her as a long-mistreated old softie. The actress has been touted since “Bridesmaids” as one of the most promising screen comediennes, but she remains very much an acquired taste that’s easy to resist acquiring. Her shtick is obvious—a sequence in which she predictably screams along with pop tunes on the car radio (by now the cliché of cliches) is simply irritating, and her early bar-party sequence is truly embarrassing. In those cases (as in her recent turn in “This Is 40”) she (and her directors) certainly don’t seem to realize that in many comic bits less is more. Of course, she’s also expected to extract laughs from her considerable girth, which gets extremely tired after awhile (as in a gag when she gets exhausted running just a few feet, although later we’re told that she’s carried an unconscious Bateman to safety—consistency is of no matter here). Fat jokes, frankly, are no longer the guaranteed winners they once were.

As to Bateman, he basically plays straight man to his co-star, and mostly looks benumbed throughout. But one shouldn’t feel sorry for a guy who’s helped produce the vehicle that embarrasses him. Everyone else in the cast is either wasted (Chestnut, Peel, and Jon Favreau, in a cameo as Sandy’s nasty boss, and John Cho, in a slightly longer role, as his new one) or humiliated (Patrick, Harris, Rodriguez and especially Stonestreet). Behind-the-camera contributions aren’t much better, though they are better than the material deserves.

Lots of things get stolen in “Identity Thief,” but the biggest heist is of the hundred minutes you’ll forever lose watching it.