“Tammy” is like a car crash you want to look away from but you feel like you can’t because you just paid more than $10 to see it. Starring Melissa McCarthy (“The Heat”) as Tammy and Susan Sarandon (“The Big Wedding”) as her alcoholic grandmother, the movie should deliver more laughs than it does.

That being said, it’s a relief to see a female lead who’s not a beach-blonde, salon-tanned, model-skinny and unreflective-of-any-normal-looking-woman babe. There are funny moments. The problem is that most of those moments are just exploiting the immaturity and stupidity of our protagonist, who is not only flawed but flat-out obnoxious. Melissa McCarthy is still funny and in many ways still channeling her “Bridesmaids” persona (even the signature left hand to wall, right hand to hip move we saw in the airplane scene). Perhaps that’s the fundamental issue: Even though McCarthy was hilarious in “Bridesmaids,” her raunchy sense of humor is only sustainable in small, pithy doses.

The film follows the journey of Tammy, who — in the first 15 minutes — hits a deer in the road, gets fired from her job at a Topper Jacks and walks in on her cookie-cutter husband having a romantic dinner with the pair’s neighbor. What next?

Tammy heads home to her mother — played by Allison Janney (“Bad Words”) — who lives two doors down, which results in a brief argument over the definition of the word “pattern.” “A pattern comes in a pair of two … It’s science!” McCarthy screams. Tammy quickly decides that she’s going to take off (somewhere) before her grandmother Pearl (Sarandon) runs out punctually to join her in a sequence of events that is both jolted and unrealistic. They take Pearl’s car on a road trip adventure. Queue the cliché existential road trip transformation.

From then on, the movie is a downward spiral, punctuated by small and trivial laughs. Each new scene forces you to sympathize with protagonists that are just plain boring.

In a bar scene, the granddaughter-grandmother pair try out their drunken powers of persuasion with a son-father pair, which turns out to be gruelingly unfunny and awkward. When the father and Sarandon hit the dance floor, Tammy joins them by galloping in circles around the dance floor. The son, played by Mark Duplass (“Parkland”), watches her improvisational dance moves with the lit eye of a man-in-love, which quickly becomes grotesquely annoying.

It’s not remotely unfathomable that Duplass’s character, Bobby, would have a crush on McCarthy’s character. But it seems like the film’s main effort is making Tammy seem like an unattractive, messy person. In the bar scene, she points out that she attracts men like “flies on shit.” It’s not until about halfway through the movie that she takes her first shower. She wears brown crocs constantly. Although it’s not imperative that a protagonist looks attractive in order to attract, the movie loses realism in its attempt to push these two together. Bobby is a caring son who runs a farm. McCarthy is an ignorant thief who just got fired from a burger joint and spends a month in jail. Perfect couple.

It’s hard to continue watching past this point. However, one of the funniest scenes in the movie occurs when Tammy deliberately leaves Pearl at a rest stop. Pearl agrees to buy beer for a young hipster couple in exchange for a ride on the back of their cruiser bicycles. When Tammy realizes — crap — she just left her drunken, diabetic grandmother in the middle of no-man’s-land, she heads back and gets in a fight with the young couple. She says to the boy, “I want you to do bath salts and eat her face off.” There’s nothing like witnessing shitty teenagers get beaten up.

Of course, we couldn’t just leave the theater peacefully before Pearl drunkenly calls her granddaughter a “fat loser.” It stings. What follows is Kathy Bates (“Midnight in Paris”) giving Tammy some supposedly motivational, punch-in-the-gut speech that didn’t contribute anything to the movie.

But if you do decide to take the leap, Dan Aykroyd (“Behind the Candelabra”) does make a funny 10-second appearance while picking Tammy up from jail. Best to just pass the time while counting how many instances the pair mention fucking the ice cream guy.

1 out of 5 stars