Being irritated is primarily the survival of Ego, Irritation or anger will exist in one way or another until Ego is gone, however; there are various degrees of it. You can see “gross anger” in someone’s face or vibrations (They get upset and their face change color and their bathing becomes heavy.) That is the irritation that perhaps you refer to and it is the most common. Some call this to be “normal,” and even HEALTHY. 🙂
In my experience the change came while I was 3 years in knowledge. On that day I became very angry with a loved one. The realization was strong, for I failed the “test paper,” of spiritual knowledge and at the same time it affected me and affected the feelings of this person who was very close and dear to me. I felt pretty bad and had the determination to stop this childish tantrum.
From that moment on, “gross” anger went away. It wasn’t shown from my face, but then my vibrations became very strong when upset, in other words, anger still was trying to express but the gross form was gone.
Vibrational anger/irritation is felt by most people around you, specially if someone has a strong field of energy. This type of anger is related with sex-lust. I recall that feelings of sex-lust and vibrational anger were somehow related. This is a process, for we need to remember that all vices are related for they come from Ego, in different shades and forms.
From Vibrational irritation/anger comes, anger in your thoughts: Someone cuts you off while driving, a thought emerges with unkind words or unkind comments for a brief time. This is subtle anger. The only one aware of it, is you. For that is important to maintain a peaceful stage “constantly.”
Spiritual life based on practical principles will definitely, help on getting rid of irritation/anger. Deep meditation helps in recognizing that peaceful state which when lost, we automatically should tend to go back to it, so it becomes “natural.”
As you can see, your question has many layers; hope that you received the answer that you were looking for,