How can I stop myself from getting so mad? I've already tried breathing techniques and it doesn't really work for me.
I'm sorry you are experiencing difficulty with anger. It's great that you want to make a healthy change. Seeking help from a professional is one of the best ways to process and manage your anger, but if that isn't an option for you right now, here are a few other suggestions:
- Reframe your anger: Instead of having an outburst or turning your anger inwards, have a constructive conversation with someone about how you feel. You might not need to speak to the person that triggered your anger in order to process it; talking to someone else can also be helpful, so long as you are working towards a constructive outcome rather than ruminating on your frustration. 
- Recognize your triggers to find better solutions: If you know that you get really worked up waiting in long lines, try to beat the crowds and run errands early, avoiding peak business hours. Or, if you have a co-worker who usually gets on your nerves, develop some strategies to minimize contact with them throughout the work day. Look for patterns in your anger and take a pragmatic approach to securing peace of mind. 
- Distract yourself:  If something happens that triggers your anger, look for a change of scenery. Go for a walk, open a new tab in your browser, or put on a favorite song while tackling chores in a different room in your home. Sometimes taking your mind off of things can help you recover more quickly.