Drawing on McCarthy's real-life experience, Tammy lives in a small Illinois town with her husband (Nat Faxon)—who cheats on her with a skinny woman (Toni Collette)—three houses down from her parents (Allison Janney and Dan Aykroyd) and grandmother (Susan Sarandon, using most of her acting chops to play up the "grandma" characteristics, like frequently re-applying red lipstick and tottering on swollen ankles). One gets the impression that all of McCarthy's funny friends wanted to be in her movie, even though they don't have much to do in it. Even Kathy Bates appears, playing a lesbian relative who tells Tammy she worked "hard" to have her apparently idyllic and quirk-filled life. The best addition to the cast is Gary Cole, playing a lascivious flame for Grandma Pearl.
Once Tammy and Pearl hit the road—headed to Niagara Falls by way of Missouri—the movie is a series of stop-and-go interludes, some of which are funnier than others and none of which (despite the movie's fumbling attempts at genuine emotion) are heart-warming. Capers include the aforementioned drunk driving, picking up men at a bar, robbing a fast food restaurant, celebrating "lesbian Fourth of July," and a fight with two underage drinkers. These episodes string together connected by little more than the dynamic duo having them.
The movie might have benefited taking more influence from Thelma and Louise, Sarandon's most famous movie involving a female road trip duo. Instead, the stakes remain low and have something to do with Tammy's need to stop being a "quitter" afraid of leaving her small town.
But it remains unclear whether the movie believes Tammy actually needs to learn a lesson. She bonds with her grandmother over sharing secrets and wreaking mayhem—most of it legitimately dangerous—and that pattern leads directly to her making new friends and the romantic pursuit of a nice guy who likes her for being herself. These sound like traditional indications of (female) success, and she only has to be slightly less self-destructive to have them.
The real lesson of the movie is not for Tammy but for the audience: that it doesn't matter whether Tammy is working toward something; that she should be accepted as she is. This seems designed as a form of wish fulfillment for women that is equally as unrealistic as the more common cliché that women should be movie screen perfection.
Tammy tries to have it both ways on the funny and heart-warming by skirting hard lessons about the necessity of hard work to living the dream and Grandma's alcoholism (in a funny-horrible scene that unleashes McCarthy's ability to sob convincingly). It touches on the consequences of Tammy's worst actions and allows her to admit her broken marriage was not "all" her husband's fault, but never allows Tammy to become mildly competent at anything.