Creator/RodneyDangerfield is Monty Capuletti, a baby photographer with a supportive wife but a tight-fisted super-rich mother-in-law (Mrs. Monahan, played by 1940s sex symbol Geraldine Fitzgerald) who despises Monty's bevy of vices (drinking, smoking, eating junk food, gambling, and some socially acceptable drugs). Not too long after his daughter's wedding (for which Monty and best friend Nicky, played by JoePesci, destroy the cake with their drunk driving), the mother-in-law dies in a plane crash. Oh, but there's a will, one which says that Monty gets the family's $10 million department store empire -- if he can go a year without indulging in his bad habits.
A subplot has virginal daughter Allison's marriage to Julio disrupted by her unwillingness to have sex (she's especially offended when Julio produces an illustrated book of sex positions to help educate her). Julio spends a few episodes of doing a very bad job trying to talk to his wife, after she moves back in with dad and refuses to speak to Julio.
Monty's brother-in-law Clive (played by Jeffrey Jones), naturally, wants Monty to fail because then Clive will get everything, but he doesn't really seem to do much other than tricking Monty into designing a line of "regular guy" clothes which get him laughed at a lot. But this humiliation, combined with the seeming abandonment of his friends (engineered by Clive, who convinced them they were a bad influence), drives Monty to give up, but just as he's headed out to get drunk, he runs into Julio, who accidentally shoots Monty in the butt -- hospitalizing Monty long enough for the year to pass and the inheritance to be his.
The year up, Monty and family celebrate on a yacht (where Julio tries to hide from Allison, who has reconciled with him and become insatiable in her sexual demands). The lawyer shows up, seemingly to finalize the inheritance, but turns out to be accompanied by Mrs. Monahan, having faked her own death to trick Monty into flying right. In the end, they all live together in a mansion, where Monty seems to have turned around to fully agreeing with his mother-in-laws views -- but then he sneaks off to join Nicky and his friends for pizza, poker and beer.
!!This film provides examples of:
* FakingTheDead: Mrs. Monihan
* MeaningfulName: The surnames of the families -- Capuletti and Monahan -- allude to the feuding families of RomeoAndJuliet, the Capulets and the Montagues (thrown in with the fact that Capuletti is an Italian-sounding name, while Monahan is Irish, suggesting a bonus CultureClash)
* OnOneCondition: Mrs. Monahan imposed one for her son-in-law to inherit her business.
-->'''Monty:''' My mother in law! For years, I wouldn't kiss her face. I ended up kissin' her ass!
* ShotInTheAss: Just when Monty has given up on his effort to quit drinking/smoking/carousing (in order to inherit ten million dollars), his daughter's estranged husband shows up with a gun, and this happens -- putting Monty in the hospital and saving the inheritance.
* TimeCompressionMontage: While Monty is recovering from his bullet wound, time passes enough for him to win the estate.
* TitleDrop: some of Monty's friends assure him of his chances using the phrase
* TitleThemeTune: By Music/BillyJoel.