John Waters said that fat was the last screen taboo—strange, in a country with skyrocketing obesity levels. The Melissa McCarthy vehicle, Tammy, directed by her husband Ben Falcone, is Waters-lite: a quite funny, warm, lackadaisical road comedy. Tammy (McCarthy) is an overgrown kid from the Midwest; she busts up her old Toyota on the same day she loses her burger-parlor job; arriving home unexpectedly, she catches her husband with the next-door neighbor lady. On the spur of the moment, Tammy decides to cut out for Niagara Falls with her drunken, bawdy granny, Pearl (Susan Sarandon), whom she barely tolerates. So: Thelma and Louise,the next generation.

Falcone does get out to the lakes and rivers and pretty, poky towns, though the trip stalls in the usual spots: jail, the posh party with welcoming relatives.

As Tammy's love interest, Mark Duplass brings his peculiar non-energy to the role. If his acting is mostly done with the eyes, the eyes here are sinister, Aphex Twin-ish—withholding chemistry. One word that sums up Tammy is "mumblecore." Is it because Duplass is nervous about a girl that big? Couldn't they have found someone who liked 'em fat like that?

McCarthy is gritty, salty and believably vulnerable and you can see why she has caught on, despite inferior movies; Tammy seems more authentic about heartland partying than a drama would have gotten. Still, McCarthy isn't an XXL comic who is conversely dainty, like Curly Stooge or John Candy. The comedy is all in the face, which makes matters televisionistic. She talks a good game—her idea of foreplay is saying "Let's light this candle" and pouncing—but if Sarandon's Pearl gets to run wild, the film is oddly modest about its heroine.  The fat taboo is honored nervously—we see Tammy in a hot tub scene wearing a wetsuit, and this happens in a movie co-starring Kathy Bates, who flashed the world in About Schmidt. Ultimately, Tammy goes therapeutic—just because the pep talks have truth in them doesn't make them less hot air.

There's much so much to encourage here, anyway. Tammy is likely to be Bechdel Test champ of the year. The rareness of a mostly female comedy attracted quality actors such as Sandra Oh, Allison Janney and a strangely formidable Dan Aykroyd. Sarandon is pretty much priceless as the out of control, Oxycontin-popping gran.

Tammy

R; 96 MIN.