Driving across the country shoulder to shoulder in a Chevy Aveo, with either your overbearing parent to your left or your patronizing offspring to your right, mile after mile, hour after hour – what could be more fun?!

As “The Guilt Trip” tediously shows, almost anything.

Seth Rogen and Barbra Streisand are not the problem in this formulaic road trip flick – in fact, the two share a nice little mother/son chemistry. Maybe that’s because Rogen, in a real shift from his usual goofball roles, plays an organic chemist. As Andy Brewster, he has developed a completely natural, totally safe and exceptionally good household product with the nearly unpronounceable name of Scieoclean, and he is crossing the country talking to buyers at Kmart, Costco, HSN and elsewhere trying to get his cleaner on their shelves or shows.

Good son that he is, he stops to visit his long-widowed mother, Joyce (that would be Babs), in New Jersey before hopping in the rental car and heading out.

While director Anne Fletcher (“The Proposal”) and writer Dan Fogelman “Crazy, Stupid, Love”) may have been distracted by other things when putting this together, the actors deftly refuse to overplay their hands and never devolve into stereotypes.

These are loving, not bickering, generations, and truthfully there isn’t much guilt here, either – just the small bit at the beginning when Joyce confesses to Andy that before she met and married his father she had a serious relationship with a man who may have been the love of her life. She named Andy after him.

A secret Google search by Andy tracks down the long-lost paramour, and in a fit of affection and curiosity, he invites his mother to ride along with him, for some together time – and, unknown to her, to meet the other Andy in San Francisco.

“You want to spend a week in a car with your mother?!,” Streisand asks in Oscar-worthy astonishment.

And then they’re off, in a budget-minded clown car instead of the SUV Andy wanted, through the snowy mountains of Tennessee, stopping in at strip clubs (yawn) and to visit old girlfriends (wow, yawns are catching), until they hit the great State of Texas, for one of the longer stops and two of the better moments in the film: One is kind of romantic when a handsome cowboy coaches Joyce on how to eat a 50-ounce steak in an hour. The other comes when Joyce finally tells off her self-pitying son, who has dismissed every idea she has offered to help the scientist in him become a better salesman: “You condescending, self-absorbed little (not very motherly word),” she says, right to his face, before tossing off another expletive she used so well in “The Owl and the Pussycat” all those years ago.

Like all road trips across America, this one eventually reaches Las Vegas, where we enjoy another five minutes of fun filmmaking as Andy makes his pitch to HSN (once the Home Shopping Network) and its hostess, played by Nora Dunn in a short but entertaining skit.

With a few profanities, the book-on-tape “Middlesex” and a PG-rated strip club, “The Guilt Trip” is one of those sweet misfires of a movie. You like the characters, they like each other, you hope for more but, despite a touching ending, it doesn’t add up to anything beyond a star-studded story you’d find on Lifetime or even Disney.

A guilty pleasure it is, unfortunately, not.