It is not unusual to observe a person explode at what appears to be a minor provocation. When the response is so disproportionate to the stimulus, most likely the anger is not at all directed toward this provocation, but it has been displaced from some other target.
For example, someone becomes angry at his employer, but knows that to express this anger would jeopardize his job. His suppressed anger continues to churn within him and intensify precisely because it is being suppressed, because the frustration of not being able to discharge it adds to its fury. Upon coming home, someone in the household says or does something trivial, and our employee erupts with a violent outburst of rage.
Irrationality borders on insanity, since both essentially deny reality. In the above case, reality did not warrant so extreme a reaction; hence, the inappropriate reaction can be considered akin to insanity.
Granted that one cannot safely discharge his anger at his boss, but suppressing the anger is not the only alternative. A few moments of rational thought might help him get a handle on his anger. He might ask himself, "Why did the boss's comment affect me so deeply? Is it because I resent the superior-inferior relationship we have? Is it because I am insecure and I am interpreting his remark as a threat to my livelihood? Is it because his comment aroused self-doubts which I have been harboring?"
Analysis of an emotion can help dissipate it and prevent us from developing a short fuse which will result in an explosive reaction.