I used to be that person that can't take criticism and blows up whenever he's challenged on something.

I wish I knew what happened, but I'm now the person who wants criticism so that he knows how he can improve himself. It still hurts my feelings a little, but that's totally drowned out by the new mission created for bettering myself. (Of course, that assumes the criticism is valid. It's not always. In that case I just contain my anger and file the advice away in case I keep hearing it over and over. If I do, that means it wasn't something to ignore after all.)