Plot

Family guy, Jack Sadelstein, prepares for the annual event he always dreads--the Thanksgiving visit of his fraternal twin sister, the needy, and passive-aggressive Jill, who then refuses to leave.

Jack Sadelstein is a successful advertising executive in Los Angeles, with a beautiful wife and kids, who dreads one event each year--the Thanksgiving visit of his fraternal twin sister, Jill. Jill's neediness and passive-aggressiveness is maddening to Jack, turning his normally tranquil life upside down.—Columbia Pictures

Jack Sadelstein is a successful ad exec with a loving wife and beautiful kids. For all this, there is one event that Jack absolutely dreads: the annual thanksgiving visit of his deranged, needy, passive-aggressive fraternal twin sister Jill, turning her brothers tranquil life on its head.—Tom Daly

We see homemade videos of Jack and Jill growing up. As the videos progress, it seems that Jack is the more gifted twin, with Jill constantly trying to get his attention by hitting him, hurting girls around him, etc. An adult Jack (Adam Sandler), a successful advertising executive in Los Angeles with a beautiful wife Erin Sadelstein (Katie Holmes) and two kids, their biological daughter Sofia (Elodie Tougne) and their adoptive Hindu son Gary (Rohan Chand). Gary compulsively tapes various objects to his body. Conversely, Jill is unemployed and lives alone in their childhood home, which she inherited following their mother's death the previous year.

Jack is incredibly irritated about the holiday visit of his "identical" twin sister Jill (Adam Sandler), as he has to pick her up at 4:00am. Following a series of problems from the airport to the house, Jack's patience is soon stretched increasingly thin. Jill's neediness and passive-aggressiveness is maddening to Jack, turning his normally tranquil life upside down.

Jill starts ruining Thanksgiving dinner. At dinner, her obnoxious behavior embarrasses a homeless guest, Otto (Allen Covert), as well as Erin's parents, Carter (Geoff Pierson) and Bitsy Simmons (Valerie Mahaffey). Jack snaps at Jill in frustration. Jill then runs away into the woods near the house with her pet Cockatoo, Poopsie. Jack's wife makes him apologize to Jill & to beg her to come back into the house.

Jill proceeds through a list of activities she has planned to do during her visit, including being a contestant on The Price is Right (she receives a variety of prizes after incapacitating herself while spinning the wheel), going horseback riding (she proves too heavy for a pony which collapses under her weight), and touring a studio. When she answers her phone in the middle of a movie, Jack reprimands her, and she exits in tears. She tells them she has an open-ended ticket, and Jill decides to stay until the end of Hanukkah. Meanwhile, Jack's client wants him to get Al Pacino to appear in a Dunkin Donuts commercial for their newest menu item, the Dunkaccino.

Jill tries online dating but doesn't get much of a response until Jack poses as Jill and alters her profile, leading her to get over 100 responses. When her date, "Funbucket" (Norm Macdonald), meets her, he runs away and hides in the bathroom.

Feeling guilty, Jack takes her to the Lakers game where Al Pacino is supposed to be, in an attempt to talk to Pacino about signing up for the Dunkin Doughnuts commercial. Pacino develops a crush on Jill as he gives her his phone number on a hot dog, written in mustard and ketchup. Jack hopes Jill would leave by New Year's Eve since Jack and his family are going on a cruise.

The staff of Jack's company, Sunny & Sadelstein, throw him a birthday party. Jill attends, but disgraces herself along with Jack and his colleagues, resulting in her ejection. Later, Pacino takes Jill to his home and lets her pick out a cake. He gives her his phone number and invites her to his home, where she accidentally destroys his Oscar statuette. Uninterested in him, she promptly departs.

The next day, Jill is leaving, until Jack's gardener, Felipe (Eugenio Derbez), takes her to the park where he has organized an entire family picnic to have fun. Jill meets Felipe's kids who are without a mom since Felipe's wife died 4 years ago. Jill immediately connects with everyone; however, after trying Mexican food for the first time, she suffers a severe case of diarrhea.

Pacino makes a deal with Jack that he will do the donuts commercial if if he gets a date with Jill. So, to ensure Jill stays, Jack asks her to accompany them for a cruise on New Years. She insists on bringing Poopsie, despite the cruise line's strict policy against pets.

At sea, Jill and Poopsie irritate everybody on-board, and Jill repeatedly rebuffs Pacino. Jack disguises himself as Jill and goes on the date with Pacino, as he still hasn't told Jill about the deal with Pacino & moreover Jill hasn't shown any real interest in Pacino every time Jack brought his name up. Pacino picks "Jill"from the ship using a helicopter and takes her to a castle.

Suspecting that her invitation was just to convince Pacino to do the advertisement, Jill phones Jack and hears Pacino in the background. Dejected, she returns home. Arriving in the Bronx on New Year's Eve, Jill discovers that the bank has foreclosed on her home after she discarded numerous bills that she mistook for junk mail.

As Jack learns how much Pacino cares about Jill, he realizes that he loves his sister, and races back to the ship. Once there, however, he learns that Jill has gone back home to the Bronx, because she figures out that the only reason Jack asked her to stay and come on the cruise was so that he could pimp her out to Pacino for his commercial deal.

Jill, now homeless, encounters a group of former schoolmates, led by class bully Monica, at a restaurant. Jack arrives with his family, and the siblings reconcile via their made-up language. At the restaurant they see an old high school classmate, Monica (David Spade) who attacks Jack's wife, but is stopped by Jill.

Afterwards, they go to Jill's house, which Felipe has decorated to declare his love for Jill. She is overjoyed that someone loves her and embraces him. Pacino arrives dressed as Don Quixote, his character in a Broadway production of Man of La Mancha, and reminds Jill that he cares about her. But he steps aside once he sees that Jill is happy with someone else.

The commercial that Pacino stars in, promotes a new coffee Dunkaccino as a rap song. Pacino hates the commercial and tells Jack to destroy every copy and threaten everyone who has seen it.