"Humongous" is horrendous, and not in an entertaining way, either. The low-budget Canadian horror dud, now at area theaters, resolutely refuses to deliver the goods, not only at the shock level, but even at the simple startle level. It takes some nerve in a time of high-tech filmmaking and sophisticated makeup tricks to grind out a horror picture in which the monster is never clearly seen until he is dead, and barbecued to a turn, in the last reel.

Director Paul Lynch also luxuriates in the weariest of all creepster tricks: lots of shots from the fiend's perspective as he peers through shrubbery at the victims dangled before him. The impression given by this trite excess is of someone on a rampage armed with nothing more lethal than a hand-held camera. The cliche' cries out for parody on "SCTV"; a deranged cinematographer could be roaming the woods secretly photographing unsuspecting picnickers, then leaping out at them with his Arriflex wildly awhirl.

Like almost every movie in the Stalking Psycho genre, this one opens with a violent incident from the past, a 1946 Labor Day rape, as it happens. We flash forward 36 years and find five squabbling teen-agers who run aground in their pleasure boat on the island where the rape occurred. The sexually repressed woman who was brutalized has died, leaving behind a misshapen hulk of a son, presumably fathered by the rapist whose fate is never quite accounted for, though when last seen he had a guard dog attached to his face.

Witlessly and lethargically, the teenies are bopped off one at a time, off-camera yet, until only spunky Sandy (Janet Julian) is left. She skewers sonny-boy with a no-trespassing sign and that's that. Ads for the film say the villain is "hungry," but what he eats are German shepherds. Human victims, he just hangs up in the basement to dry.

Lynch shows no flair, nor even any competence, for shooting action, but in the early part of the film, he does seem at home with scenes involving sexual tension among the young. The picture probably got its R rating not for violence, of which there is little, but on the basis of some mild topless sex play. On the island, one of the girls wanders off to collect berries in her bosom, thus turning her breasts a messy blue. This could be the scene that earned the movie its title.