Couples Retreat

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Dave (Vince Vaughn), a dealer for Guitar Hero, and Ronnie (Malin Ãkerman), a stay-at-home mom, are a typical couple raising two young children in the suburbs of Chicago. They experience various stresses including redecorating their house and raising their kids. Joey (Jon Favreau) and Lucy (Kristin Davis) are high school sweethearts with a smart but naive teenage daughter named Lacey. Their relationship is on the rocks and they are even considering a divorce once Lacey goes off to college. Jason (Jason Bateman) and Cynthia (Kristen Bell) are a neurotic couple who've experienced multiple failed attempts to conceive, and Shane (Faizon Love), who has recently separated from his wife, has a much younger twenty-year-old girlfriend, Trudy (Kali Hawk).
At Dave's son's birthday party, Jason and Cynthia, using PowerPoint, announce their troubled marriage and they are considering divorce because they cannot have a baby. As a last-ditch effort, they have found a couples therapy resort named Eden. A deal called the Pelican Package is half the normal cost if they can get three other couples to join them. In their presentation, they show beautiful pictures of sunlit beaches and beautiful locations. They also assure the others that the couples therapy is purely optional.
Dave and Ronnie discuss their inability to go because of childcare responsibilities and decline the trip. In the middle of the night, their home security alarm is activated when Jason shows up unexpectedly to further sell the idea of the retreat. The commotion wakes the kids, who have overheard their parents' conversations of not being able to go because of them. Fearing that their parents are contemplating divorce, the kids have already arranged for Dave's father, Grandpa Jim-Jim (played by Vince Vaughn's real-life father, Vernon Vaughn) to babysit so their parents can go to Eden.
The retreat proves to be divided into Eden West and Eden East. West is for couples and uses the tagline "Stay Together". East is for singles and uses the tagline "Come Together". East and West attendees are not allowed to intermingle.
Upon arrival at Eden West, the four couples are shown their villas. At dinner, Sctanley  [sic] (pronounced "Stanley"), the resort host (Peter Serafinowicz), informs them that couples therapy, which starts at 6 a.m., is actually mandatory. If any couple fails to attend, it will be taken as an indication that they want to leave, and a refund for Eden will be given, although not for their airfare. The group debates what to do. After an indulgent dinner with many delicacies, they decide to put up with "a couple of hours" of therapy in order to enjoy the other amenities of the resort.
In the morning, each couple meets with an assigned therapist. All four couples learn that they have problems, even Ronnie and Dave, who thought they were fine. They endure resort owner Marcel's (Jean Reno) unusual methods, including swimming with and feeding lemon sharks and yoga sessions with amorous instructor Salvadore (Carlos Ponce).
On the fourth night, Trudy escapes to Eden East. The other seven, encouraged by Joey who is unsatisfied with his marriage, leave to find her. Following an argument between Cynthia and Jason, the men and women split up. As they try to find their way to the resort, the men end up arguing and pointing out each others' marriage mistakes.
The women run into Salvadore who takes them to Eden East. The men come across the staff lounge where they find Sctanley playing Guitar Hero. He threatens to report them to Marcel, but Dave challenges him to the game (without telling Sctanley that he is involved in the game's production). Sctanley, after having lost the wager, directs them to Eden East, even though he knows he was tricked by Dave.
When they arrive, Dave realizes what a good thing he has with Ronnie. He goes with her to be alone at a waterfall. Joey finds Lucy with Salvadore and knocks him out, reuniting with his wife. Cynthia and Jason share drinks and end up becoming intimate. Shane runs into his ex-wife, who admits she still loves him. Shane tells Trudy to remain in Eden East and enjoy being single, then leaves with his ex-wife. All four couples return to Eden West.
Marcel, seeing that the couples have worked out their problems, frees them from the therapy and allows them to go jet skiing, and with that, really enjoy the rest of their vacation.

Question: Who has an argument that causes men and women to split up?
Answer: Cynthia and Jason