Anger

Anger is an emotion characterized by antagonism toward someone or something you feel has deliberately done you wrong. Anger can be a good thing. It can give you a way to express negative feelings, for example, or motivate you to find solutions to problems.

But excessive anger can cause problems. Increased blood pressure and other physical changes associated with anger make it difficult to think straight and harm your physical and mental health.

Some view anger as part of the fight or flight brain response to the perceived threat of harm. Anger becomes the predominant feeling behaviorally, cognitively, and physiologically when a person makes the conscious choice to take action to immediately stop the threatening behavior of another outside force.

Anger is an emotion related to one's psychological interpretation of having been offended, wronged or denied and a tendency to undo that by retaliation. 

The external expression of anger can be found in facial expressions, body language, physiological responses, and at times in public acts of aggression. Humans and animals for example make loud sounds, attempt to look physically larger, bare their teeth, and stare. The behaviors associated with anger are designed to warn aggressors to stop their threatening behavior.