My speech. Nothing comes close to this in the things I wish I could change. I've stuttered ever since I starting talking, which was at age three (in which my mom was told to take me to a school for the deaf because I would never speak). No one knows how embarrassing and frustrating it is when you struggle with your own name, and then have to listen to adults mock you and laugh.
That's another thing too. I wish I had tougher skin, but that's something I'm working on. I'm shy and don't speak up for myself much.