Anger is an ever-present factor of human interaction. If you don't understand anger, you don't understand a lot of what goes on between people, including between Catholics discussing their Church.
Since I don't understand anger, I'm looking at what St. Thomas has to say about it, both as an irascible passion (considered in itself, its causes, and its effects) and as a capital vice.
Anger is a peculiar phenomenon. As St. Thomas puts it, "it is a passion somewhat made up of contrary passions;" it's the one passion that has no contrary passion, but as a vice it does have a contrary, which doesn't have a one-word name but amounts to not being angry when you should be angry (that lacking anger is a vice is explained just after anger is shown to be a capital vice).
When anger arises and begins to be roused, it is called rage [or choler] .... [Ill-will]implies that the bile endures, that is to say, that the memory of the wrong abides.... Rancor, on the other hand, implies watching for a suitable moment for revenge....
St. Thomas corresponds these three kinds of anger to three things that give increase to anger. The choleric man is easily moved to anger; the passion of anger because of an excess of bile (okay, we can tighten up the biology), the vice in response to any slight cause. The sullen or ill-willed man is moved by an inflicted injury that remains in his memory -- for too long, if his anger is sinful. The ill-tempered or rancorous man has a stubborn desire for vengeance that lasts until they have inflicted punishment.
I think these three kinds of anger can all be discerned and distinguished in the heated arguments that characterize so much of on-line Catholic discussion. Some people are easily moved to anger that quickly dissipates; perhaps most everyone is, if they're having a bad day. Others feed their sense of personal injury with angry words, and still others are clearly aiming to inflict injury on their opponents.
The difference between ill-will and rancor, between anger is turned inward and anger turned outward, may not always be easy to detect, but I think I have encountered people who are clearly rancorous, who are habitually angry and habitually trying to bring down their enemies, yet who show no sign of acting out of memory of some grievance against themselves or others.