There are many different ways to define abnormal behavior. You could define abnormal behavior with the statistical definition or the social norm deviance.
One way to define normal and abnormal is to use a statistical definition. Frequently occurring behavior would be considered normal, and behavior that is rare would be abnormal. That kind of definition works fine with a behavior such as talking to others, as the two rarer possibilities would be not talking to anyone at all and talking too much to too many people—both of which would be considered abnormal.
Another way of defining abnormality is to see it as something that goes against the norms or standards of the society in which the individual lives. For example, refusing to wear clothing in a society that does not permit nudity would be seen as abnormal. But deviance from social norms is not always labeled as negative, abnormal behavior, as in a person who decides to become a monk and live in a monastery in the United States. That would be unusual behavior and not what the society considers a standard behavior, but it wouldn’t be a sign of abnormality.
One sign of abnormality is when the person experiences a great deal of subjective discomfort, or emotional distress while engaging in a particular behavior. A woman who suffers from a fear of going outside her house, for example, would experience a great deal of anxiety when trying to leave home and distress over being unable to leave. However, all behavior that might be considered abnormal does not necessarily create subjective discomfort in the person committing the act.
Behavior that does not allow a person to fit into society or function normally can also be labeled abnormal. This kind of behavior is termed maladaptive, meaning that the person finds it hard to adapt to the demands of day-to-day living. Maladaptive behavior includes behavior that may initially help a person cope but has harmful or damaging effects. For