USA TODAY September 26, 1990, Wednesday, FINAL EDITION Tough image takes toll Articulate, opinionated and unflinchingly true to her instincts and values, Sinead O'Connor seems unfazed by adversity. That's a common misconception. ''People constantly think I'm tough,'' she says. ''Even in good reviews, they say my songs are based on aggression and confrontation, just because I say what I think and say it loudly. That does hurt. I'm very strong, but I'm not aggressive.'' Another misjudgment: that she's humorless. Asked if she took offense when Andrew Dice Clay called her ''a bald chick,'' O'Connor cracks, ''I am a bald chick.'' And to the idea that her baldness lends to her stony image, she shrugs and deadpans, ''People are hairists.'' Though she sported a quarter-inch stubble earlier this year, she's taken to shaving her head clean again. ''You can't get a decent haircut in this country,'' she complains.