I wish I'd listened to Mister Rogers more when I was younger.
When I get angry, it is a full-body experience. I work hard to be rational and reasonable, and that gets easily short-circuited when I'm upset. I feel like it's a common affliction for boys and men. We're told to be strong, and stoic. We're criticized for showing emotion, or for crying. (As an aside: Crying is so damn healthy.)
If I could tell my adolescent self anything, it would be this: Get comfortable being upset. Make friends with the experience. Learn from it. Speak comfortably and openly about difficult feelings. It will be alright.