Can I insult a teacher to the point where he seems genuinely hurt?
That seems mean. Why would you insult a teacher just to hurt him?
He screwed up my kid's life by failing him.
Whatever your kid's teacher did, there is no call to insult them as it is hurtful. Make an appointment to sit down with the principal and discuss the teacher's actions instead of being antagonistic.
You don't know how much I hurt right now for my kid. I'm going to report him to the principal right now.
And you should. And hey this might help resolve the issue so your kid might not fail. At least it will be better than insulting him, that wouldn't have solved anything.