Did you know that the 'vice of anger is a perversion of that instinctive feeling that prompts us, upon attack, to resist force with force'?
There is of course a 'lawful sentiment of anger, a righteous indignation, which is the ardent, but rational desire to visit upon the guilty a just retribution.'
'Anger as a capital vice is a violent and inordinate desire for punishing others ... often anger is accompanied by hatred, which seeks not only to repel aggression but to take revenge...'
'Anger that goes as far as hatred and rancor, when deliberate and willful, is of itself a mortal sin, for it grievously violates charity and often justice.' - The Spiritual Life, Tanquerey
Be angry - but let it be without sin. - Ephesians 4:26