Home videos show fraternal twins Jack and Jill Sadelstein growing up in New York City. Jack is the gifted twin, while Jill constantly tries - and fails miserably - to get his attention by injuring him or driving others away from him.In present-day Los Angeles, Jack is a successful advertising executive who lives with his beautiful wife Erin and their two kids Sofia and Gary, a Hindu child they adopted at birth. Jill never left the working-class neighborhood they grew up in; she recently inherited the Sadelstein home, having lived with their mother until her death one year ago.As always, Jack is genuinely irritated by the upcoming Thanksgiving visit of his sister. Jill ruins Thanksgiving dinner by loudly embarrassing a homeless guest. Jack immediately lashes out at his sister, making Jill run into the woods with her pet cockatoo Poopsie. Erin demands that Jack apologize, which he unwillingly does. Jill has a list of things she wants to do while in Los Angeles: be on a game show (The Price is Right, which gives Jill a carload of prizes after she knocks herself out while spinning the wheel), go horseback riding (she proves too heavy for the pony, which collapses under her), and do a studio tour. Since Jill has an open-ended plane ticket, she decides to stay until after Hanukkah, to Jack's horror.Jack encourages Jill to try online dating, but she is unsuccessful until Jack alters her profile by putting it on Craigslist, leading to more than 100 responses. When Jill's date "Funbucket" meets her, he hides in the men's room until she leaves the restaurant.Jack's agency client, meanwhile, wants him to somehow get legendary actor Al Pacino to appear in a Dunkin' Donuts commercial to promote a new coffee called the "Dunkaccino". Jack takes Jill to a Lakers game where Pacino is supposed to be. Pacino ignores Jack but is taken with Jill and gives her his phone number. Jack hopes Jill will go home by New Year's Eve, as the family is going on a cruise. Jack's friends and colleagues throw him a birthday party, extending the invite to Jill. Again, Jill loudly disgraces herself, Jack, and the various celebrities in attendance. Pacino brings Jill to his home (where she accidentally destroys his Oscar statuette), but despite his infatuation with her, Jill is uninterested with Pacino and soon leaves.Jack's Mexican gardener Felipe, also smitten with Jill, takes her to meet his family at their annual fiesta, where she hits it off with everybody, and tries Mexican food for the first time, acquiring a horrible case of diarrhea.Pacino refuses to do the Dunkin' Donuts commercial unless Jack gets him another date with Jill; to that end, Jack invites Jill on the cruise with his family. At sea, Jill refuses to see Pacino again, so Jack disguises himself as his sister and goes on her date with Pacino. Jill suspects that she was only invited just so Pacino would do the commercial; that is confirmed when she phones Jack, he answers as Jill, and hears Pacino in the background. Pacino, still believing Jack to be Jill, spells out that he sees Jill as an unrecognized woman proud of her brother's success. Feeling guilty, Jack returns to the ship, only to learn that Jill has gone back home to The Bronx.At a restaurant on New Year's Eve, toting a picture of her and Jack's late mother, Jill comes across a group of former classmates and bullies, led by Monica, who pick up directly where they left off until Jack, Erin, and their kids show up. Jack and Jill converse in their made-up twin language (which even Jack finds incomprehensible). Monica attacks Erin and is cold cocked by Jill. Pacino also turns up at the party, dressed as the Man of La Mancha, and tells Jill that while he has feelings for her, there is another man more worthy of her than himself. Jill goes home, where Felipe and his children await her arrival. Felipe professes his love for Jill, and the two begin a relationship.The Dunkin' Donuts television commercial is made, with Pacino starring and singing a rap song. When Jack shows it to him, Pacino tells him to destroy every copy.