Victimhood is a scab that should never be picked, because the last thing the martyred want is for a wound to heal.

And there it is. You bathe in the proverbs and aphorisms of John Michael McDonagh long enough, he’s got you doing it.

“The Forgiven” is a decadents-in-the-desert parable from the writer-director of “The Guard” and “Calvary,” the brother of the more famous Irish playwright and writer-director of the Oscar-winning “Three Billboards Outside of Ebbing Missouri.”

Alternately stark and lurid, poetic and very well acted, it’s a return to form for McDonagh, who rather lost the plot with “War on Everyone.” He’s adapted a Lawrence Osborne novel, a story of infidels gathering to party in the desert — Westerners doing what they’ve long done in Morocco — until an accident sobers at least one of them up.

Londoners Ralph Fiennes and Jessica Chastain spend a bit too much time in the Tangier bar, and bars along the way, to get to a party in the middle of nowhere on the edge of the Sahara. That’s how it happens — a boy, standing in the dirt road in the pitch black night, a driver arguing over directions with his wife, an accident.

But we’ve seen the teenager having his own argument, egged on into something other than selling fossils to European tourists. We’ve seen the pistol, even if David and Jo Henninger — even their surname is alcoholic — never do.

They show up at the Baccanale tossed by the rich gays Richard (Matt Smith) and Dally (Caleb Landry Jones) with a crumpled bumper and a dead boy in the back, which barely interrupts the festivities.

Rent-boy Dally might gripe “What a bore they are, what a mess they’ve made,” but at least Richard has the good sense and character to call the police and face whatever limited music there might be for killing “a nobody” standing in the road in the middle of the night.

David’s an instant reminder that the Brits invented most of the world’s racial slurs, and probably xenophobia, too. What might the locals have in store for him? “Lynch me? Public castration?”

His American wife has had about enough of this boozy, posh poseur.

“What a nice little fascist you’ve become.”

But maybe David’s right to be paranoid. The foreigner-coddling cop wears his sunglasses at night for effect and keeps his reassurances short. Still, there’s also the matter of the boy’s father.

The stars of this movie may be two Oscar winners, with a Doctor Who and former X-Man (Jones) to boot. But the Arabic cast is what really classes it up.

Mourad Zaoui plays the Islamic aphorism-quoting Hamid, an unflappable but judgmental head servant, who shames David –“It’s the honorable thing.” — into meeting with and then accompanying the boy’s grieving Berber father (Moroccan actor Ismael Kanater) back to his distant home village to be buried. The father is a bitter, self-righteous man who seems capable of just about anything, which gives David pause, but only a pause.

And the wonderful French-Arabic character actor Saïd Taghmaoui (“Wonder Woman,” “Hate”) plays the sad old man’s translator, who might be here to comfort David, or lead him to his fate.

“The desert is what we fish,” he says of the vocation of the boy who died. “The fossils are what we catch…God is making a joke.”

The story has familiar McDonagh themes of redemption of the irredeemable and is overflowing with the tasty, testy dialogue of the witty and the damned, his family’s true gift to the cinema.

“The tongue has no bones, sir,” Hamid says, settling a boozy dinner-table argument. “But it crushes, all the same.”

“Piece by piece, the camel enters the couscous.”

You can see why McDonagh was drawn to this material, and why actors fight for the chance to work in either of the two gift-of-the-screen-dialogue-gab siblings’ movies. You’d swear Moroccans settled Ireland, or the other way round.

The film flirts with a few tropes that drag it down — sexual misadventures, a glib, uncaring and arrogant man finally feeling remorse, the idea of martyrdom as something a gentleman might find “honorable,” if told that’s “customary in these parts.”

There’s also something inherently silly in all these coddled pale-faces exposing themselves to the Saharan sun, SPF450 Brits and Americans (Chastain, Jones and Christopher Abbott) oblivious to the irony.

And making Chastain’s character’s husband a dermatologist is just, well, rich.

But you can tell McDonagh’s back on form just by the way he throws all these pearls — either cribbed from the novel, Mark Twain, or his own inventions — before us, as if there’s a never-ending supply of them. Because maybe, in his case, there is.

“A woman without discretion is like a gold ring in a pig snout,” is funnyand biting in English or in Arabic with subtitles.

“You should have a Twitter account.”

Rating: R for language throughout, drug use, some sexual content and brief violence.

Cast: Ralph Fiennes, Jessica Chastain, Ismael Kanater, Saïd Taghmaoui, Mourad Zaoui, Marie-Josée Croze, Christopher Abbott, Caleb Landry Jones and Matt Smith.

Credits: Scripted and directed by John Michael McDonagh, based on a novel by Lawrence Osborne. A Vertical/Roadside Attractions release.

Running time: 1:57