TWO spotty, ugly youths, in scruffy (and presumably malodorous) AC/DC and Metallica T-shirts, are playing couch potatoes, watching pop videos on TV. Their conversation goes something like this: ''Hey, this video sucks. Huh-huh. It's full of men dressed like wusses.'' ''Yeh, I hate things that suck. They make me puke. Heh-heh. Switch it over.'' (They channel surf and land on a thrash heavy metal video depicting very loud guitars and blonde models with very little on.) ''Huh-huh. This is cool. Huh. Those dudes are cool.'' ''Yeh. Heh-heh. And check out that chick. She wants me. Come to me, babe.'' (Cut to the two teens headbanging while humming the riff to Whole Lotta Love, then proceeding to discuss what effect the babes are having on their lower anatomy.) This is the world of Beavis and Butthead, a year ago unknown apart from one appearance in an alternative animation short, now a nightly fixture on MTV and the biggest thing in youth culture since Wayne and Garth went ''schwiinnngg!'' or Bart Simpson told Homer to ''eat my shorts''. Beavis and Butthead are crudely animated, crudely scripted characters who do nothing but be crude and perfectly obnoxious for half an hour, laugh inanely at every breath and turn scatology into an art form. The two supposedly south-western middle classyobs are nothing if not cleverly-observed representations of the Average American Teenager. Teenage viewers are seeing themselves in Beavis and Butthead - though they would probably not admit it - and making them the cult heroes of 1993. The B and B T-shirts, mugs and stickers are already on the production line and there is talk of a movie. Needless to say, God-fearing Middle America sees the cartoon series as the most serious assault on the nation's sensibilities for a good while, and has emerged from the bunkers to bombard MTV with letters of disgust. The show has been the subject of numerous moral debates in newspaper columns and TV items, and the anally-fixated, animated mates are the cover stars of the current Rolling Stone. E VEN Time magazine has seen fit to comment, a columnist claiming that Beavis and Butthead ''may be the bravest show ever run on national television''. The show is not nearly as consistently funny as The Simpsons or strips like the Far Side. But some might see a certain subversiveness in its repetitive theme - basically stuff that's cool (loud rock music, chicks and violent imagery) getting the thumbs up, and stuff that sucks (everything else) being ridiculed. There is no character development and little plot beyond Beavis and Butthead trying to outdo each other in anti-social tricks like playing baseball with a frog as the ball, or breaking wind loudly in convenience stores. If this is the face of American youth today, and the strip is quietly poking fun at everything bourgeois and socially acceptable, then - as critics would have it - God help America. The strip's creator, Mike Judge, is a normal-looking type, 30 and prematurely balding, from an average background but with a wacky, Gary Larsonesque streak that betrays a fellow whose handle on things is not quite the same as most of us. Judge was an engineer and then flirted with rock music until he started creating characters based on gawky kids he remembered from high school. A Beavis and Butthead short feature showed on an MTV animation special, and the station took a chance in signing him to produce a series. Judge writes the material and does all the voices himself, underlined by the incessant banal ''huh-huh'' giggling that has become the duo's trademark. If Time's vision of the show as ''brave'' means anything, it is no doubt due in part to the fact that these are cartoon characters like no other seen on prime time. They use rude words, overtly fondle their private parts, expose their backsides and frequently have bright green stuff emanating from their noses. In other words, Beavis and Butthead are just like average real-life teenagers, but have broken the unwritten rule that cartoon characters are not supposed to imitate real-life to such an uncomfortable extent. In this way, their prime-time presence makesBart Simpson look like a Disney character. MTV's creative director Judy McGrath told Rolling Stone that the series is partly a reaction against an overdose of political correctness. ''Beavis and Butthead came along at just the right time for comic relief. I see them as an extension of our best promos, which have always been irreverent.'' For Hong Kong residents, it is a shame - although perhaps not entirely unexpected - that MTV Asia on STAR TV has no plans to show the series, judging it a bit too off the wall for regional tastes. I have seen many a callow international school kid hanging round and showing not a little of the Beavis and Butthead stereotype. For the moment, the show will have to remain a peculiarly American phenomenon, continuing to be an irritant to the nation's moral crusaders while the T-shirts sell out, kids in every neighbourhood across the land yell ''that sucks!'' at each other and Mike Judge becomes a rich man. By the time the next, more outrageous cultural atom bomb hits the youth market, Beavis and Butthead will doubtless have been pensioned off to become mid-1990s relics on cable TV re-runs. Whether or not you think that sucks is entirely a matter of taste. EVEN Time magazine has seen fit to comment, a columnist claiming that Beavis and Butthead ''may be the bravest show ever run on national television''. The show is not nearly as consistently funny as The Simpsons or strips like the Far Side. But some might see a certain subversiveness in its repetitive theme - basically stuff that's cool (loud rock music, chicks and violent imagery) getting the thumbs up, and stuff that sucks (everything else) being ridiculed.