Spoiler alert:

The parents are clearly lying, and the abuse gets catalyzed by the mother, because of clear principles about the mother-son dynamic. It's very close to the male-female social bonding dynamic, where conflicting biological needs cause each member to constantly insult the other, most often without conscious awareness.

However, let's look at the son, too: If he's a self-unaware juice-squirter who kept the same head from elementary school, then obviously when he goes through puberty, he's going to go spasmodic and reactive. So why should anyone pity THAT person?