TAMPA: There are some lines that can never be crossed, some actions that can never be forgiven, or in the case of three Florida teens, some stop signs that can never be put back in the ground. Christopher Cole, 20, Thomas Miller, 20, and Nissa Baillie, 21, discovered that today when each of them was sentenced to 15 years in prison for yanking out a stop sign in February 1996 at an intersection where three kids later died in a car crash. Convicted of manslaughter last month, the three admitted they had stolen as many as 19 signs the night before the accident, but insisted that the fatal sign wasn't one of them. The tale did little to sway Judge Bob Mitchum, who rejected a defense request for a retrial made on the basis of a key witness's last-minute charge that the prosecution had forced him to lie. As he slashed the recommended 30 to 50-year sentence for being an "absolute waste of your life," the sobs echoing throughout the courtroom barely seemed to register with the judge, who said: "There are no winners in this case." No winners, indeed.