The film kicks off with a stark warning: "The performers in this movie are professionals. Please do not attempt to perform these activities at home. If you attempt to drink this much, you will die." We meet Jan Wolfhouse, who is engaged in a high-stakes game of quarters with another man—his father. After a triumphant flip of a coin that lands in a narrow flower vase filled with beer, Jan's father gulps it down. Soon after, Jan's brother, Todd, interrupts the beer-fueled banter with news that everyone is waiting for them at a funeral for their family patriarch, Johan Wolfhouse.
Johan, comically delivering his own eulogy via pre-recorded video while downing beers, shares his last wishes, including a heartfelt plea for his mother, his grandsons Jan and Todd, and himself. He entrusts them with a treasured German doll named "Bobo," right before yanking his own life support cord and passing away, facilitated by some dark humor.
The narrative quickly transitions to Great Gam Gam, Johan's mother, instructing Jan and Todd to take his ashes to Munich, Germany, during Oktoberfest for a traditional farewell among the family’s ancestral resting place. However, the brothers, intoxicated by the festive atmosphere, inadvertently provoke the crowd during a singing mishap, leading to a spectacular collapse of the beer tent.
In the midst of the chaos, they stumble upon Beerfest, an underground drinking competition. Initially, they are shocked to discover that Americans are grossly underestimated in this arena, having no team to represent them due to their bravado often leading to brawls. The German team, featuring Baron Wolfhouse, ultimately humiliates Jan and Todd. The brothers soon learn that Johan allegedly stole a famous beer recipe, leading them to resolve to train and return a year later for revenge.
They begin their quest by recruiting an eccentric but skilled team, including Landfill—an ex-brewer with a penchant for drinking, and Dr. Charles Finklestein (Fink), a scientist with knowledge of beer games. With tension brewing, Jan and Todd also invite Barry Badrinath, a former college rival of Todd, who surprises them by excelling at their chosen games despite past grudges.
The training montage unfolds as they prepare for the competition, characterized by outrageous binge-drinking sessions and increasingly absurd attempts to improve their skills. Eventually, they uncover Bobo's hidden beer recipe, which they brew for themselves. However, as the tournament approaches, their brotherhood is tested by personal tragedy when Landfill dies while attempting to drink a vast quantity of beer.
Despite these setbacks, they learn from Great Gam Gam that they hold the true heritage of the Von Wolfhausen family. This revelation reignites their determination to reclaim their family's honor, especially when Gil, Landfill’s twin, steps in to join the team. They finally head to Germany, disguised as a keg, to challenge their rivals.
The climax unfolds at the Beerfest competition, where Team USA defies the odds and navigates through a series of perilous drinking games, including the infamous Das Boot challenge. In a nail-biting finish, they ultimately secure victory against Team Germany, reclaiming control of their family's brewery.
As the story wraps up, the characters, now crowned champions, enjoy well-deserved leisure time in Amsterdam. There, they encounter Willie Nelson, who tempts them to join his upcoming stoner competition. The movie concludes, teasing audiences with a setup for a sequel titled "Potfest."
