I've realised in situations that are really upsetting, the more we tell ourselves we shouldn't get angry the more lousy we feel, and it usually extends the duration of anger rather than shortening or dissolving it as what we like to do.
Why not just allow yourself to feel what you feel as a natural response. If you should feel angry, then allow yourself to feel angry. But what is important here is to be conscious and aware of your feelings.
John Hill is right in saying not to allow external forces to influence us. So while we allow ourselves to be unhappy about it, use that as a temporary means to release that emotion from inside. Validate your own feelings.
It's ok to feel anger and to recognise and allow it. But it's not ok to use that anger to do something else as a retort or response. So after recognising it, do what you need to do to cool down. After that only then think of the way to respond to the event that caused you to be angry.
We can't choose the way we feel. But we certainly can choose the way we respond to it.
