Recognizing that you are angry is the first step. Acknowledge the anger and accept it. While acknowledging the anger, focus on keeping yourself centered and grounded. Remember to breathe. Feel your feet firmly on the floor. Don't judge your anger, just accept it as an important, valid emotion.

If you are telling someone you're angry you can do so in a validating (validate the other person) and assertive (state your feelings) way. For example, "I appreciate that you are giving me a ride to the store. I'm feeling angry, though, because you're 20 minutes late. Next time you are picking me up and are late would you please give me a quick call to let me know? I'd really appreciate it."

Remember to breathe and stay as grounded as possible.