Self-destructive behavior is any behavior that is harmful or potentially harmful towards the person who engages in the behavior.
Self-destructive behaviors exist on a continuum, with suicide at one extreme end of the scale. Self-destructive actions may be deliberate, born of impulse, or developed as a habit. The term however tends to be applied toward self-destruction that either is fatal, or is potentially habit-forming or addictive and thus potentially fatal. Self-destructive behavior is often associated with mental illnesses such as borderline personality disorder or schizophrenia.
Acts of "self-destruction" may be merely metaphorical ("social suicide") or literal (suicide).
Self-destructive behavior may be used as a coping mechanism when one is overwhelmed. For example, faced with a pressing scholastic assessment, someone may choose to sabotage their work rather than cope with the stress. This would make submission of (or passing) the assessment impossible, but remove the worry associated with it.
Self-destructive behavior may also manifest itself in an active attempt to drive away other people. For example, they may fear that they will "mess up" a relationship. Rather than deal with this fear, socially self-destructive individuals engage in annoying or alienating behavior, so that others will reject them first.
More obvious forms of self-destruction are eating disorders, alcohol abuse, drug addictions, sex addiction, self-injury, and suicide attempts.
An important aspect of self-destructive behavior is the inability to handle the stress stemming from an individual's lack of self-confidence - for example in a relationship, whether the other person is truly faithful ("how can they love someone like me?"); at work or school, whether the realization of assignments and deadlines is possible ("there is no way I can complete all my work on time"). Self-destructive people usually lack healthier coping mechanisms, like asserting personal boundaries. As a result, they tend to feel that showing they are incompetent is the only way to untangle themselves from demands.