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Is there anything more depressing than the thought of another movie based on a “Saturday Night Live” sketch? How about one that’s a take-off of a TV show that was considered passe long before it left the air in 1992? (It was hardly without reason that “The Simpsons” got so many laughs out of identifying “MacGyver” as the choice of old maids Patty and Selma.) “MacGruber” is basically a one-joke comedy, and the joke is too moldy to support feature length—-and told in an unremittingly coarse, crude fashion.

As played by SNL’s Will Forte, the title character is, of course, the doofus cousin of MacGyver, a guy who eschews guns in favor of home-made devices he cobbles together as needed from stuff like duct tape, sink cleaner and dental floss. But while that slim idea might support a three-minute sketch, Forte and his co-writers realized that alone it couldn’t serve a 90-minute script. So they’ve inserted the character into a parody of a old-style action flick with nods to Rambo and a wide array of other “heroes” played by the likes of Stallone, Willis and Schwarzenegger. The idea was obviously to do a variant of the “Austin Powers” formula in a different setting, ribbing not James Bond movies but the rabid American alternative.

What’s resulted is a narrative in which MacGruber, supposedly “the best there ever was” (though how remains a total mystery), is lured out of retirement to an eastern monastery by his old boss (Powers Boothe) to track down the evil genius (Val Kilmer) who’s stolen a Russian missile and who just happens to have blown up MacGruber’s new wife (Maya Rudolph) at their marriage ceremony. It’s a task MacGruber can’t refuse, but when he accidentally blows up the entire team he’s assembled from old colleagues (most played by WWE wrestlers—was Vince McMahon involved in the production?), he has to cobble together a new one consisting of just two members: a straight-arrow soldier (Ryan Phillippe) who initially idolizes him but comes to doubt his reputation; and an ex-operative (Kristen Wiig) who’s now an aspiring, if untalented, pop singer.

What follows is effectively a chain of skits in which the trio bumble their way to uncover and defuse the plot, all marked by MacGruber’s obtuseness, ineptitude, misplaced self-confidence and utter disregard for anyone but himself. It’s a depressing business for two reasons. One is that the target is so obvious. The unhappy fact is that the recent “Rambo” reboot and the new “Die Hard” installment were virtual self-parodies already, and trying to do a satirical take on the genre at this late date is an exercise as musty as “MacGyver” itself.

But if you’re going to make the attempt, is it really necessary to make your script little more than a chain of sniggering sex gags and scatological jokes, periodically interrupted by bursts of slapstick violence and male nudity? How many references to blow jobs and “dumps,” or shots of a naked derriere, does a movie need nowadays? It’s a continuation of the infantilization of humor in American comedies nowadays, most notably demonstrated in the villain’s name—Dieter Von Cunth, which is repeated so often it might as well be a mantra. That’s the level of comic invention here. Just compare a picture like “Airplane!,” which hilariously skewered the “Airport” movies but did so without continuously grossing people out. The Zucker Brothers-Abrahams humor might have been broad, but it wasn’t deliberately ugly. Who would have thought that we’d one day be praising it for its relative subtlety?

Kilmer, who looks bloated and unhappy here—at first glance you’d think he was Steven Seagal—should remember the good old days. After all, he starred in one of the post-“Airplane!” spoofs, the under-rated “Top Secret!” But he’s not the only one who suffers. Boothe has little fun with the “Rambo” Richard Crenna part, and though Wiig is very good, the material she’s saddled with isn’t. Philippe manages to maintain his dignity through most of the picture, until he’s compelled to humiliate himself during the final confrontation.

And Forte? He seems like a solid journeyman comic—the sort who’s perfect for second-string duty on “Saturday Night Live” but is woefully unsuited for leading-man feature status. Of course Will Ferrell became a star, so I suppose anybody can.

“MacGruber” ends with an over-the-top catharsis scene in which the villain is finally vanquished, and vanquished again—and again. But even there the makers can’t avoid adding a dick joke. Maybe they know their audience all too well. How sad.