Where does this anger come from? In the holy books its written that anger stems from unfulfilled desires. Buddha also spoke of the root of the problem being desires.
If everyone were supposed to overcome desires then there would be nothing to aspire for, work for or have a sense of achievement. Life would be full of mediocre stuff because no one would want variety. Just think of a world full of gray and dullness. No one wanting good clothes or beautiful women. If there was no one to appreciate stuff, why would anyone fight for it?
Now the need for everyone to feel wanted or desired makes relationships and families. Children are the root cause of the need to have relationships. Progeny, land, properties, gold, men, women, houses, animals, vehicles, weapons, etc. make for the desire to have or want.
Now when it doesn't get fulfilled then you are bound to feel inadequate.
Lets see how it holds good. If you want money, then you need to take up a job. If you are not able to land a job, your need is unfulfilled. This is bound to make you compare with others who have it. Jealousy and ill will follows suit. Then the path is completely downhill. You are unable to control anger from welling up. It grows in leaps and bounds.
Anger has roots in attachments. Even a woman getting molested can cause so much of anguish in the entire nation, that the feeling that something or someone is violated can make for the attachment. This makes the whole nation wanting to nail the perpetrator. Lynch him or murder him.
So unfulfilled desires can work up anger. Attachment to any object can create this desire. You are so much attached to your car, that even a small dent can upset us. Again if someone else gets the seat which blocks our view during the match, it creates so much anger.
I can't tell you how that anger can be removed or displaced since I just wanted to tell you how it comes up in the first place. That would be a separate topic for understanding.
So getting angry is very easy for all of us. It's getting out of it which is toughest.