Ever since stealing the show in Bridesmaids, Melissa McCarthy has been a comedy star on the rise. In an era when few if any comedians can sell a film on the strength of their names, that’s no small feat. (Whether any actors can do that anymore or if we are in a post-movie star era is a question for another time.)

Tammy is the film in which McCarthy, along with her husband and creative partner Ben Falcone, have decided to grab the reins of her career and steer it themselves. Which makes it doubly disappointing that it’s such a waste of her talents: she has no one but herself to blame for a movie that relies on schtick that has already grown tiresome without demonstrating her range.

Our first sight of her in the movie’s opening sequence puts you on warning: in a dishwater-blonde wig and a faux-MacDonalds polyester uniform, she is presented as unflatteringly as possible. Even her make-up seems contrived to make her look, well, piggy.

Let’s not mince words her: she is a fat woman. She has made that the basis of her appeal—large and in charge, and if you don’t like it that’s your problem. In a movie where she’s essentially running things (she produced the film, and co-wrote it with Falcone, who directed), she relies on stereotypes about fat people you would think she would find personally embarrassing.

Worse, unlike her characters in Bridesmaids, Identity Thief and The Heat, Tammy doesn’t rise above those stereotypes. She spends most of the film on a contrived road trip with her grandmother (Susan Sarandon, looking ridiculously good for a character who is supposed to be a lifelong alcoholic on death’s door) during which she undergoes no development. If she’s marginally less obnoxious by the movie’s end, there’s no reason for it other than that’s how we expect a comedy like this to end.

The script is so vague and meandering as to be nearly plotless: Tammy and Grandma drive around, get in trouble, hang around at a lesbian 4th of July party. It shares with Identity Thief a third act plot resolution that is unusually for a comedy, but not really all that interesting—it’s just a lazy way to end a movie in which laziness has been the major factor.

(Caveat emptor: If you go to see this because you read that parts of it were filmed in Niagara Falls, you’ll have to stay to the bitter end.)

Opens Friday at the Delevan Drive-In, Flix , Maple Ridge, Regal Elmwood, Regal Niagara Falls, Regal Quaker, Regal Transit, Regal Walden Galleria, Sunset Drive-In, Transit Drive-In

Watch the trailer for Tammy