Far be it from me to differ with Forrest Gump's mom, but ''Stupid is as stupid does'' is not a maxim that gets you very far in the aggressively ironic world of '90s culture. On the contrary, the only way to explain such diverse phenomena as Howard Stern, Ween, and Buffy the Vampire Slayer is that moronic characters can imply all manner of droll societal observations when used by creators who keep their distance. In other words, ''Smart is as stupid does'' looks to be more valid these days.
Well, not always; a movie like Dumb and Dumber in fact, Jim Carrey's whole career is a tribute to the enduring, unironic efficacy of the fart joke. But fans of MTV's Beavis and Butt-head are well aware that the show's an exceedingly sly dig at adolescent mind rot itself. Every suburban teenager knows arrested alt-rock spuds like B&B, and laughing at these guys provides proof that you're at least a little more clued in than they are.
That trashy/witty subtext was given mainstream acknowledgment in the surprised, largely positive reviews that greeted the big-screen Beavis and Butt-head Do America. Yes, opined the critics, there are pee-pee jokes here but also a genuine comic sensibility in creator Mike Judge's animated pop-cult wasteland. Perplexingly, the same critics brought out the cudgels for Tim Burton's Mars Attacks!, despite the fact that it shares Beavis' lowbrow, love-hate relationship with American junk. It may be that six seasons of Beavis and Butt-head on MTV had given reviewers a frame of reference; now on home video, though, the films look like two sides of the same scuffed coin. Both crisscross America, finding crassness, benighted self-interest, and hideous theme architecture. Heck, both use Las Vegas in exactly the same fashion: as a glitzy, so-tacky-it's-grand stand-in for the country as a whole.
Beavis and Butt-head Do America isn't quite so smart about being dumb. Still, any movie that features a hippie-dippy high school teacher singing ''Lesbian Seagull'' and that lets Engelbert Humperdinck reprise the tune over the end credits is using its noggin in nicely jaundiced ways. The ''plot'' is disposable in the extreme (our heroes are mistakenly hired by a wastrel to ''do'' his wife; they misconstrue homicidal intentions for sexual; high jinks ensue), and even the official jokes just lie there. But Mike Judge's gift is for backhanded asides, not punchlines for Beavis' muttered ''Check it out, Butt-head: port-a-potties,'' upon entering a Catholic church and spotting the confessional booths. The notebook-doodle animation is only deceptively crude, too; when Beavis suffers an accidental peyote trip in the desert, the resulting cel-block riot would do R. Crumb proud.
In its last half hour, with Beavis' obsessed alter ego Cornholio stalking the White House, B&BDA turns from spoofing teenage dimness to merely embodying it. I'd say that was a built-in dilemma with adapting short cartoons into feature films, except that Mars Attacks! also gets increasingly manic and insular as it goes. It may be the lone unintended irony of intentionally stupid movies that they're not quite smart enough to know when to quit. C+