In 2012, Donny (Adam Sandler) is a slacker who spends his time at a local strip club with his friends, bartender Brie (Ciara) and stripper Champale (Luenell). He learns that he owes $43,000 to the IRS and will be imprisoned for three years if he doesn't repay the money within one week. After drunkenly betting that an overweight man will win an upcoming marathon, Donny returns to the strip club, where he learns his son, who has changed his name to Todd Peterson (Andy Samberg), is a succesful businessman and is about to marry a rich young woman named Jamie (Leighton Meester). A TV producer called Randall Morgan (Dan Patrick) offers Donny the money he needs if he convinces Todd to visit Ms. McGarricle (Susan Sarandon) in prison for a reunion special.
Donny visits Todd, who is staying with Jamie at the house of Todd's boss, Steve Spirou (Tony Orlando). Todd is forced to introduce him as an old friend, because he claimed his parents died in an explosion. Donny meets Jamie's brother Chad (Milo Ventimiglia), a Marine, and tries to convince Todd to visit Ms. McGarricle in prison because she is terminally ill. Todd is reluctant, but allows Donny to stay at Steve's house and invites him to a cocktail party that night, where Donny meets Todd's co-worker Phil (Will Forte). Phil reveals that he's Todd's best man, but knows nothing about Todd, and passes on the role to Donny. Donny later hears Jamie yelling at Todd and realizes he isn't happy with her.
The following day, Donny attends a wedding rehearsal where Todd gets into a fight with Father McNally (James Caan) over a crude remark that Todd made towards his "dead" father. Because of this, Jamie decides that the ceremony will be held at Steve's house. Meanwhile, Donny learns Todd will be having a bachelor party and decides to join him, only to learn it'll be just a visit to a spa run by the uptight Ms. Ravensdale (Ana Gasteyer). After having sex with Ms. Ravensdale, who is charmed by his laid-back attitute, Donny convinces the others to go to the strip club with him, where Todd bonds with Brie. Eventually, everyone gets drunk, and Donny and Todd bond. They decide to go ice-skating, where Donny runs into Vanilla Ice, who hates Donny for sleeping with Ice's mother. Donny apologizes and makes peace with Ice, and the three wreak havoc through the night before returning to Steve's house, where both Donny and Ice have sex with Steve's mother while Todd dry-humps Jamie's wedding dress.
The following day, Jamie forces Todd to take the dress to the dry cleaner. Meanwhile, Donny finds a present Todd has left for him, along with a note revealing he'll visit Ms. McGarricle. Donny rushes to prison, but it's too late. Randall appears with a filming crew and Todd, believing his newfound connection with his father was a lie in order for Donny to get money, leaves in anger. Randall later cons Donny by revealing he didn't get Todd to sign a contract about his appearance, and, therefore, Randall isn't required to pay Donny.
Donny returns to Steve's home and finds out Jamie is cheating on Todd with Steve. He tries to tell Todd at the rehearsal dinner that night, but Jamie comes up with a story to cover her tracks. Defeated, Donny leaves and returns to the strip club, where Kenny (Nick Swardson), a strange man who often hangs out at the club, convinces him to earn Jamie's forgiveness for Todd's sake. Donny heads to the hotel where Jamie is staying, only to find her having sex with Chad, whom Donny learns is actually a jazz dancer who pretends to be a Marine in order not to disappoint his and Jamie's father, Gerald (Blake Clark). Jamie gives Donny the money he needs in exchange for his silence.
After talking with Brie, Donny realizes he loves Todd more than anything and interrupts the wedding ceremony with Ice's help, refusing Jamie's money and urging her to whisper the truth to Todd. However, Todd is so dumbfounded he accidentally exposes her incestuous relationship with her brother. In a fit of rage, Jamie tries to stab Todd with a knife, but is knocked unconscious by Donny. Meanwhile, Father McNally prevents Chad from attacking Donny, who leaves with Ice and Todd, who proudly accepts that he is Han Solo Berger.
A few weeks later, at the club, Donny tells Todd, who is now dating Brie, that he's ready to go to prison for three years, and intends to rekindle his relationship with Ms. McGarricle once she's released. At that moment, Donny learns that the obese man from earlier actually won the marathon and earned him $60,000 dollars, enough to prevent Donny's arrest. Donny, Todd, Brie, Champale, Ice and Kenny all celebrate together.