A “buddy picture” is a lot like a romantic comedy. The “couple” must clash, bicker or even box each other’s ears, and do it adorably. Their arguments should snap, the more stinging the wit the better.

And the leads? They absolutely positively have to have chemistry.

“Half Brothers” is a bilingual buddy picture/road comedy that fails to tick off the check boxes, starting with chemistry and stumbling through attempted jokes. And then it turns all sentimental, as if that too-sappy/too-late twist will save it.

It’s a PG-13 effort from the director of “Let’s Be Cops,” and plays like it — start to finish. Luke Greenfield seems as at a loss about how to make this funnier as he did directing Rob Schneider’s PG-13 bomb “The Animal.” This feels half-hearted, muzzled. And it’s not the least bit amusing.

Renato (Luis Gerardo Méndez) is a Mexican aircraft manufacturing tycoon who’s triggered every time somebody mentions the United States. Suggest he “expand into the US” and you’ll get an earful about “ignorant,” prejudiced, “entitled…and fat” Americans.

He has his reasons. He had a Dad (Juan Pablo Espinosa) who doted on him, built him radio-controlled airplanes even. Then the ’90s currency collapse sent Dad hiking north for work in the US. He never came home. Renato never even heard from him.

Then Dad’s American wife (Ashley Poole) tells him his father is dying. Renato reluctantly leaves his fiance (Pia Watson) and flies to Chicago, where the old man half-apologizes and, being fond of riddles, leaves his son a dying clue — “Eloise” — to explain his life.

He leaves it to his two sons, actually. That redheaded dolt Renato stumbled into in a doughnut shop? The one who so enraged him that the rich guy bought all the doughnuts so that the jerk and other “fat Americans” couldn’t have any? That’s Asher (Connor Del Rio).

Renato is more than happy to fume his way back home, his “duty” to an estranged parent done. But the fiance’ figures he could learn a few things about patience and parenting from a cross-country search for clues with the childish Asher. Renato will have a stepson after he gets married.

Renato is an aeronautical engineer. Asher is a “lazy America” stereotype, clueless about how clueless he is, mispronouncing words left and right, as a barista named “Beat Rice” (Beatrice) can attest.

Their odyssey, taken in Asher’s ancient orange ethanol-repowered Mercedes wagon, will lead them to old acquaintances of their father, from a pawn shop to convent, with Asher committing one “screw up” after another along the way.

He slips off to visit a petting zoo/goat farm, and swipes a kid, prompting irate farmers to rain shotgun pellets upon them.

“Where ELSE are you going to see goats wandering around, free?”

“I don’t know! ALL of MEXICO?”

“Hey, stop BRAGGING about Mexico!”

At every stop of their journey, they learn more about their father, the “reasons” for him abandoning his family and why he had no patience for his second son. The screenwriters, reaching for maudlin sentiment, never for one second make that case for him.

The early goat theft — they keep it for the trip — promises a more madcap romp than this script provides. I grinned at a little of the culture-clash stuff. It’s just that there’s VERY little of that. The slapstick promised by encounters with redneck bullies and the like doesn’t develop. At all.

Méndez, seen in the last “Charlie’s Angels” remake and Mexico’s “Cantinflas” bio-pic, works up a fine lather as the irate straight man here. But Del Rio, a veteran of the “Key and Peele” sketch comedy series, goes for Zach Galifianakis-annoying here. But he isn’t comic enough to turn a dull script witty and can’t make his scenes with Méndez set off sparks.

I’d say “Half Brothers” half works, but that’s unjustifiably generous.

MPA Rating: PG-13 for some violence and strong language

Cast: Luis Gerardo Méndez, Connor Del Rio, Pia Watson, Vincent Spano, José Zúñiga, Bianca Marroquin, Ashley Poole and Juan Pablo Espinosa

Credits: Directed by Luke Greenfield, script by Jason Shuman and Eduardo Cisneros. A Focus Features release.

Running time: 1:36