Which term best describes a strong feeling of being upset or annoyed?

The term that best describes a strong feeling of being upset or annoyed is "anger." Anger is an emotional response typically associated with perceived wrongs, injustices, or threats. It arises when individuals feel that their needs, rights, or expectations have been violated. This emotion can manifest in various intensities, from mild irritation to intense rage, often motivating individuals to take action or express their feelings.

Frustration, while related and often accompanied by anger, specifically refers to the tension and displeasure that stems from being blocked from achieving a goal. It is not as robust as anger itself but can lead to feelings of anger when the blockage is significant. Fear and sadness represent different emotional experiences; fear relates to a sense of threat or danger while sadness pertains to feelings of loss or disappointment. Thus, anger distinctly captures the idea of feeling upset or annoyed, making it the most accurate term in this context.