Those with deep pockets sometimes have shallow hearts. The post-college lurch before the life that waits ahead can be a panic zone. And the only shocking revelation in The Nanny Diaries is that there’s not one sprig of chest hair to be seen on a shirtless Paul Giamatti. (Certainly no one with a beard so bushy could be as bare as a baby boy, so we’re guessing he got a wax.)

Giamatti’s torso fuzz isn’t all that seems to have been forcibly removed for this adaptation of the best-selling novel. In it, a harried New Jersey college grad turns to caring for the son of a snooty New York couple that cares only about its child’s future and their own individual pampered lives.

Two former nannies, Emma McLaughlin and Nicola Kraus, wrote the book, and whatever sharp satire of emotionally detached, over-privileged families that snapped on their pages feels snipped from the movie. It’s harmless, but toothless, working through usual romances, conflicts, resolutions and physical comedy (right down to a bathtub fart, but not from whom you might expect).

Aside from a requisite big break, or reuniting with their American Splendor lead Giamatti, it’s hard to know what co-writers/co-directors Robert Pulcini and Shari Springer Berman saw here. They made the page-bound life of comic-book artist Harvey Pekar come alive in Splendor and give Nanny an interestingly floral visual distinction that’s about the only thing to watch for.

Still, as a story, anybody could have tossed off a piffle like this.

Giamatti and Laura Linney play Mr. and Mrs. X, the case-study nicknames given to a fat-cat couple in whose employ Annie Braddock (Scarlett Johansson) finds herself. After Annie saves young Grayer (Nicholas Art) from a park accident, Mrs. X mishears her name as “nanny.” On a whim, Annie postpones her uncertain future as a just-graduated business major for a temporary job that, deep down, caters more to an observational nature she developed with an anthropology minor.

Soon enough, though, Annie commits a cardinal sin of nanny-dom — saying three little words to the little man. After all, she’s Grayer’s only ally in a life filled with Mom’s all-day seminars and shopping and Dad’s out-of-town trips for work and infidelity. Throw in a fling with a studly Harvard Hottie (a charming Chris Evans), and Annie’s life seems dictated before it even really begins.

Johansson seems to know she’s in a comedy, albeit one scattershot in tone, but nothing of how to put that across with laughter given her stiff, ineffective expressions. Linney dresses up, barks terse orders and stifles tears, while Giamatti offers an extended cameo, in which his face isn’t seen for a time. For the second time this summer, Julie White (Transformers) steals a movie in the matter of about three scenes, playing a bubble-headed leader of one of Mrs. X’s many mommying seminars.

Although it finds its footing occasionally after a truly awful start, Diaries is the worst kind of throwback — to the usual red-nosed, bleary-eyed bluster that came standard issue for chick-lit flicks before In Her Shoes and The Devil Wears Prada made them safe again for both genders.