Your friend assures he’ll arrive at your place at 12PM, but he doesn’t. That’s no fault of your own, but you still get upset and angry at it, because it didn’t meet your expectation. You already expected your friend to arrive at 12PM, but he didn’t.
You created the expectation through your friends words. But he didn’t keep it. So, you get angry.
This is pretty difficult situation for us. Your friend assures you to be at your place first, and then he doesn’t arrive. But then you get angry.
Here, the root cause of anger is expectation.
Your main concern should be about living in tranquility.
For that, you’ll need to manage your expectations. Most of us are aware of our own expectations, but not aware of other peoples forced expectation on us.
Being aware of our expectation and not expecting is relatively easy, compared to other people’s forced expectation on us - for example, your friend not arriving at time s/he said s/he would.
Stop taking those expectations. It’s difficult at first because you don’t realize it. You don’t realize it because you are not expecting it yourself, your friend forced it upon you.
So, the first step is to be aware of expectation you set through your friends, and then managing them.
If not, you'll waste time being angry, when you can afford to live only for a limited time on earth.