Miles Raymond is an aspiring – but unsuccessful – writer, a wine aficionado and a divorced, depressed, borderline alcoholic middle-aged English teacher living in San Diego, who takes his soon-to-be-married actor friend and former college roommate, Jack Cole, on a road trip through Santa Ynez Valley wine country. Though still recognized on occasion, Jack's acting career appears to have peaked years ago, when he had a role in a popular TV soap but now does commercial voice-overs and plans to enter his future father-in-law's successful real estate business after he's married. Miles wants to spend the week relaxing, golfing, enjoying good food and wine; however, much to Miles' consternation, Jack is on the prowl and wants one last sexual fling before settling into domestic life.
In the wine country, the pair visit Miles' favorite restaurant, The Hitching Post II, and meet Maya, an attractive, intelligent waitress with whom Miles is casually acquainted. Jack senses that Maya is interested in Miles, who downplays his friend's intuition, and tells Jack that Maya is married. He tells Maya that Miles' manuscript has been accepted for publication, even though it is only being considered. Later, at a tasting in a local winery, they meet an attractive wine pourer named Stephanie, who is also acquainted with Maya. Jack is immediately attracted to Stephanie and arranges a double date, to include Miles and Maya, and tells Miles that he learned Maya is no longer married ("sans rock", as he describes it). During the date, Miles gets drunk and telephones Vicki, his ex-wife, after learning from Jack earlier that day that she has remarried. They return to Stephanie's home, where Jack and Stephanie immediately adjourn to her bedroom for sex, while Miles and Maya connect through their mutual interest in wine. Maya tells Miles that she is finishing her master's degree so she can leave serving and work in the horticulture industry. Miles tells Maya about his book and gives her a copy of his manuscript. As the week progresses, Jack's affair with Stephanie continues, to the point where he believes he's falling in love with her; he bonds with her daughter and makes the suggestion to Miles that they move there for him to be closer to Stephanie. After spending the day together, Miles and Maya return to her apartment and have sex. The next day, Miles lets it slip that Jack is to be married. Disgusted with the dishonesty, Maya dumps Miles and tells Stephanie who, furious and devastated to learn she's been used, breaks Jack's nose using her motorcycle helmet and hits him repeatedly.
On finding out his manuscript has been rejected again, Miles drinks heavily and causes a scene during a wine tasting when the server cuts him off, and ends up trying to drink from the spit bucket. That night, with Stephanie gone, Jack hooks up with another waitress named Cammi, who recognized him from his acting career. Hours later, Jack shows up back at the motel room he shares with Miles – naked and confessing that Cammi's husband came home early while she and Jack were having sex. Jack explains he was forced to flee without his clothes and wallet (which contains a pair of irreplaceable wedding rings). Jack convinces Miles to drive him back to Cammi's house and sneak inside, where he discovers Cammi and her husband having sex. Miles spies Jack's wallet, grabs it and runs from the house, barely escaping Cammi's irate husband, who pursues him in the nude. To explain the broken nose and cover up the infidelity to his fiancée, Jack runs Miles' convertible into a tree, giving the appearance they had been in an accident. The pair return to the home of Jack's fiancée, where he is welcomed with open arms, and Miles drives away in his battered car.
Following the wedding ceremony, Miles runs into his ex-wife Vicki and meets her new husband. After learning that she is also pregnant, Miles accepts that he will never get Vicki back. Alone, he drinks his prized wine, a 1961 Château Cheval Blanc, from a disposable coffee cup at a fast-food restaurant and falls into an even deeper depression. After some time passes, Miles returns to the routine of teaching school; coming home one afternoon, he receives a voice-mail from Maya, who says she enjoyed his manuscript and invites him to visit. Ultimately, Miles is seen driving back to Santa Ynez and knocking on Maya's door.

Question: What makes Jack drink too much and cause a scene at the winery?
Answer: His manuscript was rejected.
Alternative answer: finding out his manuscript was rejected