People who grow up in our
society learn quickly to hide their real
weaknesses, the things that would break them if found and exploited by a malicious person. When you first meet somebody, all you know about them is what they
broadcast to the world. Things that they either consciously
display, are unable to
hide, or don't know that they're showing. In school, before the defenses have fully set in and the callouses have been built up, these obvious properties can still be taken advantage of, and cause
deep pain in the hands of the
cruel.
Upon reaching maturity, all of the powerful emotional damage vectors go beneath the surface. You need a lot more than "faggot" or "fatass" to wound a mature person. Instead, it takes knowing who they are, and which of their past failures hurt the most. It takes finding the one part of their psyche that they can't bear to have fun made of. It takes being able to see the world through their eyes, and know their thoughts in your mind. In short, it takes becoming close to them.
What's more, people stop expecting pain when it's been absent for a long time. When you know that the things that hurt you in high school no longer hurt at all, you tend to think that you're somehow above being hurt at all by the words of others -- that you've outgrown placing such value on what others think. So when it happens, when somebody says words that crush you alive, part of your response is surprise that it could even happen at all. The fact that it happened at the hand of somebody close -- who is the only person who could have done it anyway -- makes the surprise even more vivid.
The urge to destroy something beautiful (which we all get sometimes, don't we?) is so much more powerful and dangerous in adults than in kids, for this reason. Because the destroyer is somebody you know and trust (and love?), and the words are crafted so precisely to burn your soul, the damage can be profound. That's why I've always had to concentrate on the fact that people are not my personal playthings, because I know that if I forgot it in anger and spoke the words that I know would affect them, they might never be the same, and I would doubtless lose them forever. I would feel vindicated with wrathful anger for all of thirty seconds, and then I would be crushed with guilt for possibly the rest of my life.