Thirteen years ago, when Vince Vaughn was all Adam’s apple and venomous verbal rattle, Trent, his hipster persona in “Swingers,” delivered a cautionary warning to his buddy and fellow fledgling actor, Mike, played by Jon Favreau.

“I don’t want you to be the guy in the PG-13 movie everyone’s really hoping makes it happen. I want you to be like the guy in the rated R movie, you know, the guy you’re not sure whether or not you like yet. You’re not sure where he’s coming from. Okay? You’re a bad man. You’re a bad man, Mikey. You’re a bad man, bad man.”

Reunited for the fourth time on screen since the iconic “Swingers,” they’ve descended with “Couples Retreat” into the sort of lazy, fatuous PG-13 movie Trent exhorted against. For most of this decade, it’s been a steady regression by Vaughn into a typecast mold of a snarky, lethargic caricature of his seminal “Swingers” role. Vaughn has settled into an onscreen deportment reminiscent of the average Joe on a Monday night CBS sitcom. Even when the movies are decent, you’re still left wondering where the exuberant presence went. Favreau, who is a much more interesting director (“Elf,” “Iron Man”) than actor, has morphed since his “Dinner for Five” phase into a physique resembling Kimbo Slice. It’s the duo of MIA and MMA — they used to be money; now they’re just getting paid.

Opening with a lively title sequence from Jarik Van Sluijs, with Bowie’s “Modern Love” bopping along to short bursts of old home movies and archival B-movie footage, this soft lob for the common megaplex quickly succumbs to a tepid script written by Vaughn, Favreau and Dana Fox. It’s a treatment so banal and humorless it’s conceivable it was thought up and scribbled down during a solitary weekend retreat. (Favreau, who wrote “Swingers,” should be particularly shamed.)

The strained, basic story is that an anal-retentive husband and wife on the verge of divorce (Jason Bateman and Kristen Bell) cajole three other couples in Buffalo to vacation at an exotic resort specializing in reinvigorating relationships. In a confounding scene, Bateman’s character, named Jason, snoops around Dave’s (Vaughn) house at midnight, tossing pebbles at the second-story bedroom window. Dave reaches into his nightstand, retrieves a handgun, loads a clip into it, and steps gingerly down his stairs, until Jason sets off the house alarm by opening an unlocked sliding door. Dave has his gun drawn on his friend Jason, and then the light comes on. Silly and hopelessly clichéd, but disconcerting and certainly never examined for all of its implications. The scene pointedly underscores how the film teeters unsteadily from attempts at comedy to poorly broaching subjects such as friendship and intimacy. The movie also doesn’t begin to explain how four couples from Buffalo – with barely seven day’s notice in the middle of winter — secure a week-long vacation in the South Pacific that was not a traditional holiday week. Without any intervening exposition, the couples are shown inexplicably docking at a pristine mountainous island, which is actually Bora Bora. “Welcome to Eden,” the staff heralds to the couples, and it appears to be a salutation which greeted the cast and crew as well. But don’t worry about continuity; it’s not long before we have the beauty described with a “screensaver” joke. “Couples Retreat” is hackneyed, disjointed storytelling in an ignominious feature film debut from director Peter Billingsley (Ralphie from “A Christmas Story.”).

The slyly witty Peter Serafinowicz plays the manager of the resort as Christopher Lee as Mr. Roarke, (It would have been fun to see his character enhanced; “Scaramanga, will you do the fandango?”) His biting delivery is undercut with a scene which unnecessarily ruptures logic. Three of the four couples are anticipating a week of frivolity but their plans are replaced with a rigorous schedule of counseling sessions and day-break exercise classes devised by the resort’s founder (the utterly professional Jean Reno). But why are they handed their itinerary booklets at dinner? Wouldn’t it have been simpler and more practical to have this document placed on the living room tables in their palatial rooms?

Despite a few decent lines, the movie’s main characters are unlikable, unformed or boring. Favreau and Kristin Davis are especially unappealing as the disconnected couple who have raised a teenaged daughter, blown off a marriage, and spend the trip on the make for younger, more desirable partners. A sequence where each is finagling for a more erotic massage in adjoining rooms is predictable and feeble. Malin Akerman plays the sitcom worthy role of hot wife to Vaughn’s regular dude. It was a stretch to call the limber Silk Spectre in “Watchmen” an actress; here, she recites every line with the emphasis of a kindergarten teacher. The rest of the cast don’t resonate, generally because there’s no real connection between the characters and the humor is perfunctory.

But “Couples Retreat” is graced by one genuine comic superlative. Every appearance by Salvadore, the amorous, good-natured yoga instructor, is hilarious. A Puerto Rican soap opera star and best-selling musician, Carlos Ponce is perhaps most recognizable for a season-long role on the WB’s “7th Heaven.” But this will become his signature role with a highlight reel of physical comedy. Salvadore struts with a mischievous grin in a Speedo hugging his chiseled body and dramatically flicks his stringy Romance novel cover boy hair. He wraps his frame around the stretched and posed bodies, both male and female, willfully dry humping his class. Ponce is an ebullient scene stealer before he’s even uttered a word; his cheeky smile a rare exhibition of merriment in the film.

Sadly, Salvadore is a supporting character so he surfaces only occasionally, while Vaughn predominates, never more frustratingly than in an overly-long boat sequence with a stupid shark attack in the island’s lagoon. The torpid scene seems stretched out merely so that Vaughn can spout like Vaughn, but he’s just a seashell of himself so it’s hollow, brusque and just bad, man. It may not be a low-water mark, but it begs the question, “How low can you go?”

For Ricky Gervais, the opposite may be true. With two smart, mature, and funny films in quick succession, he’s positioned himself as one of the leading practitioners of clever, adult comedy. After his tremendous portrayals in “The Office” and “Extras,” you wouldn’t have been surprised if he’d transferred his mordant comedic sensibility to his movies. However he’s developed a knack for noticeably lighter and fundamentally entertaining works which are still substantial. In David Koepp’s “Ghost Town,” he helps foment a 1950s throwback flair with Tea Leoni and Greg Kinnear. Directed and written by Gervais and Matthew Robinson, “The Invention of Lying” is similarly suffused with intellect, wit and belly laughs as one humble man inadvertently discovers dishonesty. Set in a modern-day community redolent with the ambiance of a New England college town, it’s a world where fibs don’t exist and deceit is unfathomable. There’s no feigning platitudes or insincerity. Unfettered by decorum, co-workers, waiters and even passersby spout out exactly what’s on their mind. Every conversation is brutally frank, making truth the world’s oldest confession.

Gervais stars as Mark Bellison a screenwriter for Lecture Films, a company specializing in the exposition of history; but not as re-enactments. Instead, in a world devoid of imagination, a camera simply films authoritative narrators such as Nathan Goldfrappe (a splendid Christopher Guest) sitting in chairs reciting bland copy. Lecture writers are designated centuries; the smug, sartorial Brad Kessler (a sneering Rob Lowe) has the 20th. Mark is lumbered with the 14th century; the Black Plague features prominently in his works.

Entirely by accident, and known only to him, the recently fired writer utters the first ever lie, to a bank teller. Initially, Mark’s skill is utilized in the most rudimentary of pursuits: money and women. But he seems more than enthralled by the prospect of his power than actually fulfilling his wishes, except when it comes to his unrequited love (a first-rate portrayal by Jennifer Garner). When he invents the afterlife in an attempt to calm his mother’s fears – and Gervais delivers a deeply moving performance in a genuinely touching scene — he’s overheard and his concept of heaven propagates. Acolytes camp out in front of his modest apartment building, quietly waiting for more information. Reluctantly, Mark delivers a tale to a world-wide audience which is an unmalicious satire of Christianity. As he divulges more edicts with the help of a facetious visual gag, the inquisitive gathering clamors for more details about everlasting eternity; there’s a succor borne every minute. “The Invention of Lying” is filled with the satiric underpinnings and dexterity of an Ealing comedy but not the full bloodedness. Both “The Invention of Lying” and “Couples Retreat” have happy endings. But only Gervais, in a bright and jocular film, has taken the care to earn it.