Anger

A personality trait that makes people hard to live with is anger. Wikipedia says this about anger.

Anger is an emotion related to one's psychological interpretation of having been offended, wronged, or denied and a tendency to react through retaliation. Sheila Videbeck describes anger as a normal emotion that involves a strong uncomfortable and emotional response to a perceived provocation. Raymond Novaco of UC Irvine, who since 1975 has published a plethora of literature on the subject, stratified anger into three modalities: cognitive (appraisals), somatic-affective (tension and agitations), and behavioral (withdrawal and antagonism). William DeFoore, an anger-management writer, described anger as a pressure cooker: we can only apply pressure against our anger for a certain amount of time until it explodes.
Anger may have physical correlates such as increased heart rate, blood pressure, and levels of adrenaline and noradrenaline. 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. The English term originally comes from the term anger of Old Norse language. Anger can have many physical and mental consequences.
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. Rarely does a physical altercation occur without the prior expression of anger by at least one of the participants. While most of those who experience anger explain its arousal as a result of "what has happened to them," psychologists point out that an angry person can very well be mistaken because anger causes a loss in self-monitoring capacity and objective observability.
Modern psychologists view anger as a primary, natural, and mature emotion experienced by virtually all humans at times, and as something that has functional value for survival. Anger can mobilize psychological resources for corrective action. Uncontrolled anger can, however, negatively affect personal or social well-being. While many philosophers and writers have warned against the spontaneous and uncontrolled fits of anger, there has been disagreement over the intrinsic value of anger. The issue of dealing with anger has been written about since the times of the earliest philosophers, but modern psychologists, in contrast to earlier writers, have also pointed out the possible harmful effects of suppressing anger. Displays of anger can be used as a manipulation strategy for social influence.

Scientists are studying the causes and effects of anger, and here are links to some of their research.

The act of describing a feeling such as anger may have a significant impact on the body's physiological response to the situation that elicits the emotion, according to research published June 5 in the open access journal PLOS ONE by Karim Kassam from Carnegie Mellon University and Wendy Mendes from the University of California San Francisco.