Plot summary

Tammy (Melissa McCarthy) is an overweight, potty-mouthed, bad-luck-prone, lower-working-class woman who is having a horrible day. On her way to work at a fast-food place called Topper Jacks, she hits a deer while shes looking for Chapstick in the backseat of her car. Once she gets there, her boss Keith (Ben Falcone) fires her for showing up late and looking like a mess. Her nose is bloody from the car accident.She heads back home, but her car dies. She eventually gets home and finds her husband Greg (Nat Faxon) eating a romantic meal with their neighbor, Missi (Toni Collette). Upset, Tammy leaves and walks two doors down to her parents' house.She tells her mother Deb (Allison Janney) that she's leaving town and shes taking her grandmother Pearl's (Susan Sarandon) car. Her grandmother insists on going too. She not only has a car, she has thousands of dollars in cash, while Tammy has only $68, plus change. She and Tammy don't get along at all. Deb doesn't want them to go because Pearl needs her medication and they were planning on putting her in the Brookview Retirement Home.Pearl convinces Tammy to lighten up and have a beer. Tammy doesn't want to drink and drive, but Pearl insists. Soon, they're doing drunken donuts in a grassy area.The next morning, they wake up near a park and Pearl convinces Tammy not to go back home and finish what she started. Pearl has always wanted to go to Niagara Falls. Tammy goes jet skiing, while Pearl drinks more booze on the dock. Tammy crashes and they have to pay for the broken jet ski. So they do, but they take it with them.They head to Louisville, for the best barbecue in town, according to Pearl's cousin Lenore. There, they meet Earl (Gary Cole) and his son Bobby (Mark Duplass). Earl is smitten with Pearl and they have sex in the backseat of Pearl's car. Bobby and Tammy awkwardly sit outside while it happens, but eventually Bobby has to head home and take care of his mom. Earl is still married, but his wife is dying and they have some sort of arrangement.Earl, Pearl, and Tammy head back to the hotel and Tammy is locked outside the room while Earl and Pearl continue touching private parts.The next morning, an angry Tammy decides to leave a still drunk Pearl so she knows what it feels like to be abandoned. When Tammy was a child, Pearl was her best friend, but stopped coming around. Tammy calls her mom, who is worried because Pearl didn't bring her medicine. Tammy turns around and finds Pearl inside a liquor store mixing whiskey in a Slurpee. The cashier is mad because Pearl keeps drinking inside the store and he calls the police.They leave and we find out that Pearl was also in the process of buying beer for minors. Tammy tells the minors to run off, there's a fight and the police show. Tammy and Pearl are arrested. Pearl pays for Tammy's bail, but Pearl is stuck because she also had a bag full of illegal Oxycontin.Tammy asks her family for money, but doesn't tell them Pearl is in jail. No one will pay, so Tammy robs a local Topper Jacks for the rest of the money. During the robbery she bonds a little with the two employees Becky (Sarah Baker) and Larry (Rich Williams).Tammy heads back to the police station to bail out Pearl, but she's already free because Earl took care of everything.Tammy and Pearl go back to the hotel and the Topper Jacks robbery is on the news and there's a pretty good description of Tammy's shirt and vehicle towing the jet ski. Pearl makes Tammy return the money to Topper Jacks the next day. Becky is there, but says Larry took the day off because he was still shook up a bit.Pearl and Tammy meet up with Lenore (Kathy Bates) who blows up Pearl's car because Tammy is now a fugitive. They go back to Lenore's house where she and her girlfriend/life partner Susanne (Sandra Oh) are getting ready to throw a giant 4th of July party. Pearl apologizes for her behavior and explains that she quit coming around when Tammy was a kid because she got drunk and made a pass at Tammy's dad and was embarrassed.Tammy asks that Pearl promise not to get drunk. During the party, they have a Viking funeral for the jet ski, sending it out onto the lake in a flaming raft. Earl and Bobby show up. Bobby tells Tammy that he digs her, but Tammy explains that shes still married and feels weird about that.A drunk Pearl starts to make a horrible toast over the PA and Tammy tries to stop her. Pearl calls her a fat slob and says she sees why Greg left her. Angrily, Tammy responds that at least she didn't try to fuck her son-in-law. Its heated. Tammy storms off. Lenore finds her and tells her that she needs to get her own life together because she can try to take care of Pearl.The next morning Tammy finds Pearl in a lawn chair dead. Everyone is crying, but it turns out that Pearl was actually just passed out hard. She gets up, they call the EMTs take make sure she's okay. The cops show up as well. Tammy fits the description of the Topper Jacks robber and there was a call about the burning jet ski the night before. Tammy goes to prison.38 days later, Tammy is released from prison and her father (Dan Aykroyd) picks her up. He offers to kill Greg for her. She declines the offer. She brings up that she knows Pearl made a pass at him. He dismisses that and says that she made a pass at everyone, but the only person who ever took her up on it was the ice cream man (who Tammy also had a little bit of hanky panky with).Tammy goes home and finds that Greg and his mistress have packed Tammy's belongings. She walks down the street to her parents' house and finds out that Pearl is now living in Brookview Retirement Home after all.Tammy goes to Brookview to break out Pearl, but Pearl is actually happy there. She's dating one of the guys there. However, they do still take a trip to Niagara Falls. Bobby shows up and he and Tammy finally kiss. Tammy tells him she decided she'd like to move to Louisville and be closer to him.There are a few scenes during the credits......Missi leaves Greg for Keith because he now owns a few Topper Jacks franchises.Tammy hangs out with Becky and Larry from the robbery.And finally, there's an alternate take of the opening scene when Tammy gets fired.