Readers should look near the beginning of chapter 9 for this answer. Chapter 9 is one of the chapters that is narrated by John, and John admits that Lorraine is correct about John's feelings toward Norton. John hates Norton. John then attempts to explain why Norton has become such a complete jerk. John thinks it has something to do with the fact that Norton used to play with dolls when he was kid. Norton eventually got old enough to realize that, according to gender norms at the time, that wasn't something boys should do, so he stopped; however, the rest of the kids continued to tease him about it. Norton went a bit "berserk" about it and turned into a "tough guy" that beat everybody up and called them "sissies."
But the kids used to make cracks about him, so that made him go berserk around the age of ten. He was the only berserk ten-year-old in the neighborhood. From then on he turned tough guy all the way. He was always picking fights and throwing stones and beating up everybody. In fact, he got so tough he used to go around calling the other guys sissies.
Norton also has a chip on his shoulder from being caught shoplifting. His entire score was a bag of marshmallows, so now people refer to him as "the Marshmallow Kid." Norton can't stand that.