The ostentatious Steins are the bad guys in “Keeping Up With the Steins,” a film that examines various bar mitzvah options for wealthy Benjamin Fiedler (Daryl Sabara) and concludes that honoring family and tradition is more important than competing with the big spenders next door.

But this is a lesson it takes Benjamin’s Brentwood, Los Angeles, family – especially his father, Adam (Jeremy Piven) – a while to learn. Throughout most of the movie, Dad’s blowing a gasket trying to match the “Titanic”-themed coming-of-age bash the Steins just threw for their son, a cruise-ship extravaganza featuring mountains of ice cream and a live reinterpretation of “Hava Nagila” as “Have a Tequila” by a well-known rap artist.

The film proposes there are better ways to enter manhood, offering a mildly offensive cross-cultural comparison in the opening scene, which has Benjamin watching a television documentary about the rites of passage – hunting, surviving in the wild – once endured by Indian braves. If only it were this easy in his tribe, Benjamin complains in voiceover, launching a tepidly satirical summary of the modern bar mitzvah.

Benjamin nearly gags on the Hebrew syllables of his recitation; his movie agent father and stay-at-home mother (Jami Gertz) debate on where to seat celebrity guests like Catherine Zeta-Jones; a party planner tries to impress the Fiedler team with a photo of her work – a performing killer whale wearing a yarmulkeh – which prompts Grandma (Doris Roberts) to lob in a joke about Shamu being Jewish. Oy gevalt.

Rarely straining for anything beyond the easy, obvious laughs, and often failing to get those, “Keeping Up With the Steins” briefly profits from the arrival of Irwin (Garry Marshall), the long-lost grandfather Benjamin’s never met. He pulls up outside the gate in a creaky RV, New Age girlfriend (Daryl Hannah) in tow: a suitable if somewhat modest entrance for that stock character of sentimental movies, the eccentric sage who reminds everyone else of the im portant things in life.

The indomitable, wisecracking Irwin is a granddad cliche, not to mention an utterly unconvincing hippy; but Mr. Marshall plays him with so much chutzpah that neither seems to matter. (At one point, he draws a sword on a hothead driver with delightful abandon.) Unfortunately, Irwin left the family behind when Adam was still a boy, which means he can’t set foot in the house without being dragged into a schmaltzy tale of forgiveness and the power of familial love. Irwin has done everything he can to make amends, but Adam, who’s gotten along just fine in adult life without a father, stubbornly keeps him at bay, despite the fact that he and his grandson obviously click. Benjamin desperately wants everybody to get along; fortified by his affection for his grandfather and the knowledge that his sins, as his rabbi nicely puts it, will soon belong to him and not his parents, he decides to use his bar mitzvah to bring the Fiedlers together once and for all.

In the end, “Keeping Up With the Steins” is a film obsessed with the perfect bar mitzvah, just not in the way its title suggests. It is obsessed with the perfect family, too. The Fiedler clan consists of a loyal, unobtrusive grandmother; a bighearted grandfather made wise by experience; a sweet, cherub-faced boy; and a mom (as played by the lovely Ms. Gertz) who seems to have stepped out of a dream. The only bad apple is Adam, a childish, domineering father who’s far more unsavory than screenwriter Mark Zakarin or director Scott Marshall seem to realize.

Adam, who spills emotions far more sloppily than anyone else, is poorly scripted – no successful agent would ever be so bad at concealing his insecurities – and poorly acted too. In Mr. Piven’s self-conscious and off-key performance, the character becomes the same kind of nasty, uptight presence that nearly spoiled all the fun in Mr. Piven’s last memorable big-screen effort, the otherwise hilarious “Old School.”

Then again, this combustible middle-aged character and the actor who plays him might just be confused: What’s a guy like this doing at the center of a movie narrated by a 12 year-old boy and full of enough pre-chewed humor and pat assurances to virtually guarantee it a spot on the retirement home circuit? He’s the odd man out at his own family reunion. No wonder he’s obsessed with the Steins.