Much of this dark farce, about the chaos that erupts when a buttoned-down milksop (Matthew Broderick) slips the Cable Guy (Jim Carrey) 50 bucks for free premium service, verges on the unwatchable; it's an uneasy hybrid of vulgar slapstick and nightmarish comedy-of-mortification, and its modest ambitions are entirely subordinate to Carrey's manic mugging and capering. But it soars above the plebian rudeness of DUMB AND DUMBER by virtue of a few moments of excoriating brilliance. Although first-time writer Lou Holtz Jr.'s awkward script could easily have been played for light laughs, director Ben Stiller (REALITY BITES) consistently brings out its darkest implications. One keenly edited sequence intercuts Carrey's vigorously lewd karaoke rendering of Jefferson Airplane's "Somebody to Love" with Broderick's seduction by a wanton young woman (Misa Koprova). At once amusing and appropriately discomfiting, it's a perfectly balanced construct that could be toppled by a single false cut, and isn't. Carrey's Cable Guy, his personality formed entirely by TV, is the neediest nerd of all time, and his dismantling of Broderick's ordered life is in the classic tradition of anarchic comedy, complete with undercurrents of class-based hostility and homoerotic menace. A cruel clown, Carrey puts the belligerent libido back in the sexless spazz character perfected by Jerry Lewis, and exploits teasing as the socially condoned form of torture it is. In all, about a third of the film (most of it contained in three extended sequences) is audaciously funny and genuinely disturbing. The rest will sorely test the devotion of Carrey's fans.