Sometimes people say or write shit that is so mean and so deeply insulting, you don't even get mad. You don't even want to argue. It may just hit you the wrong way, and other times you wouldn't care. And you don't want to show that you do care, so you turn away so no one can look at you. But your heart has dropped into your stomach and given you that sick feeling, and there's this heat rising up the back of your neck.
And you'll think of an appropriate comeback, 2 days later when it doesn't matter anymore. That's just the nature of things.