''You're tearing me apart,'' Jim Stark (James Dean) howls at his parents. For the new kid in school, it doesn't get any easier. Though he finds a friend in the extremely troubled Plato (Sam Mineo), Stark gets into it on his first day with a gang of bullies, in a knife fight and later in a chickie run. Dean was a refreshing change from the well-scrubbed teens of earlier Hollywood films. Here was a character young audiences could finally recognize.