This origin is descriptive of hostile people, because they are their own enemy.
Hostility is a term used for the build up of anger.
This response is the result of multiple minor annoyances that accumulate to a boiling point. People who are hostile are those who are tense and uptight even when they are smiling. Although they have a tendency to be extremely critical of others they are sensitive to slightest criticism. Arguments often occur over trivial matters. When the body is constantly functioning in this hostile mode, the immune system is weakened.