Protect your own and respect those of your friends. Use a joke instead of an insult, reason instead of anger, discussion instead of screaming. Use your feet instead of your fists and walk away. When you're angry at someone, tell them. When you're feeling mean, don't act.
Anger has a place.
Meanness does not. And stop picking on your sister. Lots of people give up. Be someone who doesn't. If you told Jenny that you'd go to her birthday party but later Alicia asks you to her party on the same day, go to Jenny's and send Alicia a card.