Annoyance is an unpleasant mental state that is characterized by such effects as irritation and distraction from one's conscious thinking. It can lead to emotions such as frustration and anger. The property of being easily annoyed is called petulance.

Various reasons exist for why one finds particular stimuli annoying. Measurement of annoyance is highly subjective. As an attempt at measurement, psychological studies on annoyance often rely on their subjects' own ratings of levels of annoyance on a scale. Many stimuli that one is at first neutral to, or even finds pleasant, can turn into annoyances from repeated continued exposure. One can often encounter this phenomenon with such media as popular music, memes, commercials, and advertising jingles, which by their very nature are continually repeated over a period of weeks or months.

A study published in the International Journal of Conflict Management found that one's response to an annoyance, at least when the perceived cause is another person, escalate to more extreme levels as they go unresolved. It also found that one was more likely to blame the party who was causing the annoyance in the study, rather than one's self, for the annoyance as it escalated.