Simon Rex and Ashley Tisdale star in the latest and worst addition to the “Scary Movie” franchise. (Photo by Quantrell D.Colbert)

Scary Movie 5” must be some kind of psychological experiment. Perhaps the filmmakers sat in a lab, rubbing their temples while wondering aloud how awful they could make a movie and still score at the box office.

It’s the only reasonable explanation for this lazy, boring, vile and tragically unfunny attempt at a horror-film spoof that is sure to kill brain cells and may signal the impending apocalypse. It’s the kind of movie that leaves audience members partially lobotomized, exiting the theater and muttering absently to themselves, “How on earth did this movie get made?”

The answer: cheaply. Each of the increasingly terrible “Scary Movie” installments has enjoyed an impressive return on investment, so it’s only logical that producers want to keep making them, quite literally, ad nauseam. The cost-cutting is evident, between the not-so-special effects and the amateur editing errors, including a casual relationship between dialogue and moving mouths.

Thirteen years after the first “Scary Movie,” this new chapter follows the same general template, with one exception: This incarnation kicks off with Charlie Sheen and Lindsay Lohan, playing themselves, preparing to make a sex tape.

From there, the story skips to couple Dan (Simon Rex) and Jody (Ashley Tisdale), who inherit a trio of youngsters after the demise of the kids’ dad (Sheen). What follows shouldn’t be confused with a plot; it’s more a series of snippets in which the characters borrow familiar story lines from other movies, including “Mama,” “Inception,” “Black Swan” and “Rise of the Planet of the Apes.”

But “Scary Movie” doesn’t really put any kind of twist on these familiar plots, so much as present them in some brainless context. But stupid doesn’t necessarily equate to funny, and that goes for Heather Locklear, dressed as a pregnant ballerina whose water breaks all over a male dancer’s face as he lifts her above his head.

The movie is so appalling that even a film fan who guffawed her way through “The Aristocrats” would feel nothing but a deep emptiness as the end credits begin to roll, wondering if one solid joke was too much to ask from a movie that bills itself as comedy.

But no, there’s nothing worthy of even a small smirk. Instead, the movie serves up violence against man, woman, child, doll and ape, not to mention sexual situations involving a German shepherd, a hairy, overweight nanny, Santa Claus, an automatic swimming pool cleaner, a pony and a microwave. A knock-knock joke told by a 6-year-old would be funnier than this endless stream of flatulence jokes, feces-infused food items and gratuitous vomiting.

For some reason, watching this movie kept conjuring up the voice of Smokey Bear intoning “Only YOU can prevent forest fires.” It must be a sign from beyond that we — the film-going public — have the power to end this. As long as people keep watching these inept films, the “Scary Movie” franchise will thrive and reproduce. And that is a truly terrifying prospect.

No stars

PG-13. At area theaters. Contains crude language, brief nudity, sexual situations, allusions to drug use and gory, if obviously fake, violence. 85 minutes.