When she played Tootie back in the '80s, Fields learned The Facts of Life. In the '90s, she needs to learn the facts of fashion. "I love being a tomboy," she has said, "but I also love being very feminine." Trouble is, she isn't doing either very well. Whether saggy in sweats or glammed in sequins, Fields, 25, stretches the seams of good taste. On Living Single, Kim plays a stylish boutique buyer. Maybe she should simply stay in character.