While Nicolas Cage has been building a well-deserved reputation for making an unconscionable number of terrible B movies, John Travola has been more quietly running him a close second. The latest entry under his belt is “The Fanatic,” a ludicrous mad-fan opus from Fred Durst (the lead singer of Limp Bizkit, who actually has the effrontery to include an in-joke about the band in the movie), in which he plays an autistic movie buff who takes his favorite Hollywood action star prisoner in his own home after concluding that the guy has insulted him—and by extension, all his devotees.

The result is another embarrassing exhibition for Travolta (“and you thought ‘Gotti’ was bad”), and an excruciating experience for the audience—one that will cause you to laugh and then feel guilty for doing so. That’s because the actor’s character, simply named Moose, is so terribly written and execrably played that the performance becomes a cruel insult to autistic people in general.

Moose is an implausible figure to start with—an overgrown man-child who lives alone in a dingy place supposedly near the touristy streets of Hollywood (though the picture was actually shot in Alabama), where he supposedly ekes out a living as one of those costumed folk who amuse passersby. It’s difficult to believe, though, that his shtick as a London bobby (or is it a Keystone Kop?) would earn him enough to survive for a weekend.

But Moose is principally a fan, and especially a fan of Hunter Dunbar (Devon Sawa), supposedly an action-movie hero—so much so that we see him going into debt to buy a vest Dunbar wore in one of his flicks from a collectibles shop. He intends to wear it on a special occasion: his only friend, a paparazza named Leah (Ana Golja)—who delivers narration that’s alternately banal and pulpy-purple—is sneaking him into a party where his idol is supposed to make an appearance.

Dunbar doesn’t show up—and Moose is hustled out of the place for being obnoxious and odd anyway—but he gets another chance to meet the star at a book signing. That turns into a bust, too, when Hunter suddenly leaves, ignoring Moose’s pleas for recognition in the process. Leah comes through again, however, effectively providing him with Dunbar’s home address. She tells him not to go there, of course. Fat chance.

The result is a confrontation—or series of them, actually—that show Dunbar to be pretty much an insufferable jerk who orders Moose out of the neighborhood. Also not a very alert fellow, as he fails to notice Moose creeping around his house when he returns (or the corpse he’s accidentally left in the back yard). He even manages to let Moose tie him to his bed and taunt him with accusations about not being considerate enough of his fans (presumably it’s his drug use that leaves Dunbar such an easy target).

Their tête-à-tête concludes with a twist that’s meant to be ironic, but is simply twisted instead, though it’s apparently intended to show that Moose has finally stood up for himself, not just with Dunbar but with the nasty street punks (Jacob Grodnik and James Paxton) who have been bullying him for years, trying to get him to collaborate in their pick-pocket activities—as if he could ever master the technique.

This would be awful stuff under the best of circumstances, but these are not the best of circumstances. The script, based on a story idea by Durst, is a virtual catalogue of loose ends, illogicality and lousy dialogue, down to the flashbacks that provide a bargain-basement psychological explanation for why Moose is such a sad case and the cartoon inserts that act as pointless diversions.

It’s impossible to accept Sawa (whose career seemed to tank after the “Final Destination” franchise) as a star of any wattage, or any of the members of the supporting cast as real people. But of course it’s Travolta on whom your eyes will inevitably be focused, and just as in “Gotti,” he puts on a truly killer example of bad acting in capital letters. At a time when one has the option of seeing what a performer with a condition like Down Syndrome can accomplish on screen (in “The Peanut Butter Falcon”), the caricature that Travolta offers of an autistic man here is truly grotesque, a monument to insensitivity.

From a technical perspective “The Fanatic” is competently made (Conrad W. Hall was the cinematographer—not to be confused with his father, the late great Conrad L.), but no amount of expertise behind the camera could compensate for the atrocities being perpetrated in front of it.