Our culture views anger as evil. It does so because anger is disruptive and uncomfortable and our culture sees anything that is disruptive and uncomfortable as bad. For the most part, our culture is right in saying that most displays of anger within it are wrong, but not for the reasons listed above. So let's look at anger and when it is and is not appropriately displayed in the Christian.
First, we must realize that anger exists in us when we feel an injustice has been committed, and that anger within itself is actually a good and righteous emotion to have. You won't hear that from too many pulpits, but the fact of the matter is that is exactly what anger is all about. Hence, when God is jealous (jealously being a type of anger), this isn't something evil, but good God is expressing, as it is in the context of betraying God to worship other gods, and His anger/jealousy is a result of the injustice being committed. So anger is a good thing, but it can be, and is, easily distorted.
It is distorted, not because there are two kinds of anger, but because our views of justice are warped. Instead of seeing justice in terms of what we do to God and those who represent Him, we view justice selfishly, and as narcissists define it as anything that does not give us what we expected to receive. As the kings and queens that we believe we are, we have a sense of entitlement and have come to believe that others, including God (if not especially God), have the obligation to give us the respect, sacrifice of themselves, and love due to us. When they do not, the feeling of anger begins to rise, as we sense an injustice to have been committed.
Now, notice something about this. Our culture is a very angry culture for one reason alone. We believe that we are gods. We worship ourselves and believe that all others ought to worship us, including God. We believe that when we are not worshiped, we become jealous and angry with our subjects for not fulfilling their obligations to us. Notice, then, that we have stolen the right of God for ourselves. We have reapplied the command to worship no other gods beside Me (YHWH) to worship no other gods beside Me (me). When someone does not act loving toward me, or cuts me off in traffic, or does not show respect in some way toward me, I become angry, as these people are being unjust toward me.
The greatest crime of all, however, is the one that God commits toward me when He does not give me the respect and sacrifice He is so obligated by my divine status to give me. If God does not make my life the way that I had always wanted it to be, or gives me a bad day, month or year, I grow angry at His lack of worship toward me in lavishing upon me the things in life that I wanted. If my life does not look like the American dream, it clearly is God's fault, since He can do anything, and hence, has committed an injustice toward me. I am then justified to go out and sin against God to make up for what He has deprived me, since that will display my anger toward Him for not giving me what I deserve.
Anger, then, is twisted by our false religion of the self. The very reason why people in our culture are so angry is because we are so hedonistic. We are self worshipers. It's not due to too much caffeine, or too much media, or too many people. Don't lie to yourself. It has to do with our view of ourselves and our sense of entitlement. When that is not fulfilled in the way we think it should be, anger, the rightful emotion that is spawned by injustice, is twisted to become unjust.
It is unjust precisely because the rightful heir of all respect, love, sacrifice, and obligation to worship is God, not us. He is the one who is entitled to all of what we think we are entitled. Injustice has to do with Him first and foremost, and if it doesn't, it isn't unjust. That includes the way that other humans are treated by us. We are to treat them as we would be treated (not necessarily as we are by other narcissists), since humans are made to be the image of God and represent Him. We do what is right to God by doing what is right to others.
But what does this mean for our anger? When is anger ever justified? Obviously, if God is the primary recipient of what is just, then when God, or those who represent Him, do not receive justice, our love and worship of God should cause us to become angry. In fact, if we are not angered by injustices toward God and others who represent Him, it means we do not view the world correctly and we are without true love.
In First Corinthians 13:6, Paul tells us that "love does not rejoice in unrighteousness, but rejoices in the truth." Notice, it does not rejoice in unrighteousness (adikia = injustice). It is not happy with injustice, i.e., it is angry with it. Instead, it rejoices in the truth. It is interesting here that Paul contrasts what is unjust with what is true. I believe he does so simply because believing what is true is doing justice to God, which is why so much of the Scripture harps on this point. To believe what is false is to practice injustice toward God, as God is known and glorified in the truth and robbed of what is due Him by the falsehoods we believe.
So it is when God is robbed of what is rightfully due Him that righteous anger occurs. Hence, Christ is not displaying some wayward emotion that is inappropriate to deity when He becomes angry and cleanses the temple from the moneychangers, who have turned that which was meant to be a house of prayer (i.e., a house where people commit themselves in devotion toward God and offer up themselves to Him) into a place for their own profit (i.e., a place to receive for themselves). Instead, Christ rightly becomes angry at seeing the injustice.
Likewise, when we see someone who ought to be treated as the image of God being treated poorly, we ought to become angry. When we see someone turn themselves into a dog and shun the image of God they were meant to be, we ought to become angry. Hence, we may still become angry at the guy who cuts us off in traffic and be justified for it, simply because he is endangering his and other people's lives; but if it is because we think to ourselves, "How dare you cut me off! Who do you think you are (i.e. in relation to me)," then we are exercising an unrighteous anger because it is an anger born of self worship and entitlement, and not of love for God and others.
Hence, when Paul tells false teachers to go castrate themselves (a very angry comment), he is in the right to do so, as these people are both robbing God from the glory He would receive in the truth and damning men to hell with a false gospel. Thus, all who preach a false gospel should enrage us accordingly. All false teachers should bring us to anger in their arrogance. Again, if they do not make you angry, then I would simply ask, Where is your love for God and others? Where is your sense of justice for those you supposedly love to receive what is rightfully due them?
Anger is a reaction toward what is viewed as not right. As such, how we view what is right dictates the reasons for which we become angry. I hope that we do, as Paul commands, and let ourselves "be angry and do not sin" (Eph 4:26, note that this is a conjunctive kai "and," meaning that anger and not sinning are possibly compatible). In other words, be angry for the right reasons, not for unrighteous reasons.
Anger is only blanketed as a sin in our culture because it is viewed as emotionally disruptive to our otherwise tranquil existence, and thus, it is seen as unloving, but this is just false. Anger is not the opposite of love, and is even sometimes the only right response love can give in a particular situation. To be sure, outbursts of anger that are not controlled and are self-focused display no control over ourselves and are evil. Anger born of self love, in conflict with love of God and others, is always wrong, as it evidences our self worship. Anger due to fear of loss for the self also falls into this category. But if anger is born of love, how can it be wrong?
So love God and others and be angry. If you find yourself angry for the wrong reasons, don't try to change the mere practice, as the larger problem is the lack of love and worship of God in your life. Unrighteous anger is only a symptom, then, of our idolatry. Hence, repent of that, turn toward God in faith through Christ and His selfless sacrifice, and receive the grace that gives birth to love of God and others. You may still show anger after you do, but it will be for the right reasons.