It's an emotional state that can be caused by external stimuli through thought and can trigger a range of emotions, from frustration to anger.

When someone is easily annoyed, we refer to it as irritability.

A 1997 study by Dean Pruitt, John Parker, Joseph Mikolic found that when someone else is the source of an annoyance, the frustration tends to grow if the issue isn't addressed. It also showed that as the annoyance builds, people are more likely to blame the other person involved, rather than themselves.

Carl Jung and Hermann Hesse suggested that the negative feelings we experience toward others, like annoyance or hatred, may reflect our concern for our own insecurity. According to them, we project our own flaws onto others, avoiding the discomfort of confronting those same traits within ourselves.