Rated PG-13 but best-suited for five-year-olds, “Scary Movie 4” demonstrates that a bad idea can always get worse, even worser. And in America, films based on these ideas escalate to number one at the box office. But then the concept behind each of the four installments of the “Scary Movie Trilogy” — spoofing other carelessly unimaginative films that don’t deserve the buttloads of money they make — isn’t the real root of the problem. In truth, watching films like “The Grudge” and “The Village” getting skewered on the big screen gives one a fun, pleasant sensation of justice. The bad thing, predictably, is that “Scary Movie 4” gets lost in its silliness and base appeals at laughter, thereby drowning any clever, satiric jabs in a dull sludge of idiocy.

There’s not really anything in “Scary Movie 4” that might fall under the category of “plot.” Instead, the film moves across a loosely-connected pastiche of parodies, knocking down as it goes the likes of “War of the Worlds,” “Saw,” and yes, that horror of horror films, “Brokeback Mountain.” (What a politically-correct implication in the idea that an award-winning movie about gay cowboys belongs in a lampoon alongside other works labeled “scary!”)

Some might say that the “narrative” is meant to revisit Cindy Campbell (Anna Faris), the clumsy, naive heroine of the first three films. But she, along with 80 percent of the cast, is really only there to look pretty, unknowingly tell puns and fall down after getting hit in the head by balls. Other “Scary Movie” alumni return to spew their usual, uninspired dialogue about life in a horror movie: ainnumerable deaths, throws around her caricature black sass where it’s (in)appropriate. Anthony Anderson, also black, makes gangster jokes and strips to reveal his beer belly and copious cellulite. Ivory-haired film-parody icon Leslie Nielson revisits his role as the oblivious President Harris and somehow finds a reason to take off all his clothes, too.

The only face both new and significant belongs to Craig Bierko, who plays construction father and deadbeat dad Tom Ryan. Alternately clad in tight-fitting jeans and Prada shoes (perhaps the most subtle reference to His Craziness Cruise), Tom watches his world crumble when a Dakota Fanning-look-alike daughter and angst-ridden son are dumped on him moments before a giant iPod morphs into a death-dealing tripod. (Can you say “literal”?)

If “Scary Movie 4” succeeds at all, it does so by extrapolating the right visual details from the targeted films. The “Saw” spoof might make us laugh at the unreasonable dinginess and painfully bad lighting of the scary basement. The Japanese house from “The Grudge” could not be more of a ridiculous attempt at creating a spooky atmosphere. “The Village” was always just a few steps from an interstate highway, so why did anyone ever believe otherwise? Even the fatal fall scene from “Million Dollar Baby” gets treated with hyperbolic foolishness, though the gaudy green robes and slow-motion shots perfectly match the ones in the occasionally melodramatic original.

And yes, some of the jokes can get away with being called “funny.” Favorites include President Harris’ suggestion that some kindergartners read a book called “Rumpel-foreskin” and Anthony Anderson’s claim that he plans to put a seemingly profound statement on his “myspace.” Also, Molly Shannon’s minor character makes just the right face when ex-husband Tom tells her she looks good pregnant, which, of course, she isn’t. Perhaps it was meant to be a comeback for when she renamed him “Horace P. McTitties.”

But that’s basically as good as it gets in “Scary Movie 4,” which, to those of us who can legally buy tickets for it, isn’t very good at all.