It is most likely that someone who is quick to anger in an intense way, has experienced unfairness, injustice, or maltreatment that has negatively affected their self esteem. Let’s take a person who has been bullied growing up and has decided that that is never going to happen to them again. Their coping mechanism may be to defend themselves immediately and with a high degree of intensity.
The problem here is that they have sensitivity to being mistreated. Their reaction is most likely out of balance with the incident. For example, someone accidently bumps into them and doesn’t apologise. The offended party gives them a threatening look as if to say “do you want to fight right here right now” or says “what the hell is the matter with you, you idiot”
If irritability levels are high then it may not take much for someone to overreact or allow go past a threshold from which they cannot return.
Anger is an important emotion and at times can be useful. It can serve to help us problem solve in an emergency and it can be a precursor to take action. It can help us to uncover hidden goals and direct us to more fulfilling endeavours. It can open up our awareness to unresolved pain and Trauma. Accepting our anger helps us to focus on what we might wan to act on instead of being fearful of acting out.