Party-loving Rick Gassko, portrayed by Tom Hanks, lives a seemingly carefree life as a bus driver for a Catholic school. However, his world takes a significant turn when he decides to pop the question to his girlfriend, Debbie Thompson, played by Tawny Kitaen. The engagement news sends shockwaves through Rick's tight-knit group of friends, led by the boisterous and rather immature Jay, who is obsessed with breasts and makes a living as a photographer. Joined by ticketing agent Gary, car mechanic Rudy, waiter Ryko, and Rick's brother, the disgruntled proctologist Dr. Stanley "Stan" Gassko, the friends concoct plans for an unforgettable bachelor party to celebrate Rick's new chapter in life.
Stan, already unhappy with his own marriage to the uptight Dr. Tina Gassko, sees the bachelor's party as a chance to unwind and indulge in the elusive pleasures of life—namely, the presence of scantily clad women. Meanwhile, Debbie's wealthy and traditional parents are horrified by her engagement to Rick, viewing him as an unambitious prospect lacking any real career stability. In a desperate bid to intervene, Debbie's father joins forces with her ex-boyfriend Cole Whittier, who devises a scheme to tear the couple apart, even offering Rick money to abandon Debbie. However, a steadfast Rick refuses to be swayed by these temptations.
As the story unfolds, Debbie finds herself in doubt about her choice of partner after a conversation with her cousin, Ilene, who warns that "men are pigs." While she attends a bridal shower, Rick heads to the bachelor party, promising to remain faithful and steering clear of hookers—a decision that foreshadows chaos. What begins as a well-intentioned celebration soon spirals out of control due to Cole's nefarious meddling. Cole tracks Gary, who has unwittingly hired hookers, and manages to redirect them to the bridal shower, creating a spectacle that both shocks and bemuses all the women present.
The situation deteriorates further when Ilene, who previously stashed away the "naughty" segments of a movie found in Jay's car, is left appalled when the guys are left with no entertainment. Meanwhile, Cole, with ulterior motives, trades Rick's commitment for the allure of his Porsche, only for Rudy to swipe the car for a joyride. The party escalates hilariously as the guys pull a prank at the girls' event involving an inflatable penis hidden within a sandwich, all leading to more mischief that fuels the growing hilarity of the evening.
As the night wears on, and the bachelor party evolves into a full-blown affair with countless hookers infiltrating the scene, the drama intensifies when Debbie and her friends decide to get their revenge by dressing up as hookers in an attempt to catch Rick in a compromising position. Their plans take an unexpected turn when they encounter a bouncer who mistakenly believes they are sex workers, unwittingly leading them to a Japanese businessmen's party before they manage to escape.
Chaos reigns supreme as allies become adversaries, leading to a wild, raucous time marked by drunken antics and reckless decisions. Friends' marital woes, mishaps with misguided romantic pursuits, and misunderstandings create a tapestry of riotous moments, including a particularly awkward event involving Rick's friend Brad and his botched attempts at self-harm.
The bachelor party descends into utter chaos as unexpected visitors—including a donkey that accidentally consumes illicit substances—join the festivities, leading to hilarious and disastrous consequences. The might of Rick's bachelor bash does not go unnoticed, culminating in a dramatic police raid that sends shockwaves through the partygoers.
In a dramatic twist, the evening spirals into a confrontation between Rick and the manipulative Cole. A high-stakes chase unfolds, culminating in a climactic fistfight that unfolds in synchronization with a similar scene from a 3D movie, leading the audience to believe that they are witnessing a remarkable cinematic effect. Rick emerges victorious, reunited with Debbie just as the whirlwind of events comes to a close.
Finally married, Rick and Debbie embark on their honeymoon adventure, driven away in the very bus Rick once used to drive schoolchildren, courtesy of a laughing Brad—an apt conclusion to a night filled with unrestrained fun, fleeting temptations, and the solidifying bond of love.
