It’s a relief, after the wretched Identity Thief, to see movies whose makers love Melissa McCarthy as much as audiences do. Identity Thief's comic centerpiece was predicated on the idea that McCarthy having sex is a hilarious gross-out, like she’s the pie Jason Biggs once had to diddle. Half an hour later, McCarthy’s defiantly horny slob got a makeover and a new wardrobe, and the movie presented this new, softened-up McCarthy as if it had discovered something we didn’t already know: This crazy woman’s actually worthy of love!

We know, you idiots. I swear, if I ever see Identity Thief walking down the street, I’m going to kick it in the crotch.

Paul Feig’s The Heat, a much funnier comedy than Identity Thief, had something of the opposite problem: It loved McCarthy so much that her every mad blurt and ad lib seems to have made it onto the screen, even the ones so explosive that they wrecked the film’s sentimental wrap-up. Like the Marx Brothers, McCarthy in her comic mode bucks conventional narrative structures. Who could take seriously the movie’s late claim that McCarthy’s Detective Mullins was the best cop in Boston, when she wrecked half of Southie in her first scenes? And why waste our time on such sentimental nonsense when she could be crashing through the rest?

Tammy also loves McCarthy too much, but it’s obliged to: Her husband did direct it, after all. Trouble is, it has all the problems of The Heat and only a quarter of the laughs. Here, McCarthy — who co-wrote with director Ben Falcone — plays dumb rather than badass. Her Tammy is a small-town schlump so addlebrained that she attempts mouth-to-mouth resuscitation on the deer she hits with her Corolla. (Tammy was too busy wolfing down Cheetos to watch the road.) She has never heard of Neil Armstrong, doesn’t know how to pronounce “Mark Twain,” and decides the best way to scare up a couple grand in a crisis is to hold up a fast-food joint. When you see her gliding along on a Jet Ski, you know she’ll be crashing it immediately, which might be why Tammy doesn’t even bother showing exactly what happens, opting instead for sloppy cutting and some screams.

Even if all that were funny, Tammy would still be a tough sit. Falcone’s film is an unsteady mix of broad comedy and indie heart, asking us first to roar at Tammy’s ignorance and outrageousness and then to be moved at this lovable misfit muddling toward love, maturity and a better life. It’s like if Sideways starred Ron Burgundy: Who could believe in his minor emotional growth?

Over the course of a road trip with her hard-drinking grandmother (Susan Sarandon), Tammy gets loaded while driving, scraps with some teenagers over beer, off-roads a Cadillac through a national forest and twice winds up in jail, all while shouting rote one-liners such as “This is some X-Files shit!” and “This is some Falcon Crest shit!” and “Dukes of Hazzard style!”

Meanwhile, we’re meant to be invested in her increasingly dramatic spats with her grandmother. At a Fourth of July bash thrown by a pair of wealthy lesbians played by Kathy Bates and Sandra Oh — “lesbian” is the only trait Oh is given to play — Tammy demands that her grandmother not drink. (Why anyone would think an open-bar Fourth would make a good first night of sobriety remains one of Tammy’s mysteries.) Grandma imbibes, Tammy confronts her, and the ugly truths that spill out prove absolutely insignificant: Our heroine’s on the run after that fast-food heist, after all, so — as she might ask — why are we watching this Little Miss Sunshine shit?

Bates gets one excellent scene doling out straight-talk life advice to Tammy, but McCarthy’s character is so cartoonish that I wasn’t sure why Bates’ would bother. At that party, a (slightly) made-over Tammy warms up to Mark Duplass’ Don, a handsome lug who’s smitten with her despite the fact that she’s always yelling or getting bitten by raccoons. She fends off his advances, saying she needs to work on herself, and this, of course, only entices him more.

I’m glad the movies finally get that people love McCarthy. Too bad this particular one never shows us why we should love Tammy.

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