"a marked and persistent identity disturbance is almost invariably present. this is often pervasive, and is manifested by uncertainty about several life issues, such as self-image, types of friends or lovers to have, and which values to adopt. the person often experiences this instability of self-image as chronic feelings of emptiness or boredom.
interpersonal relationships are usually unstable and intense, and may be characterized by alternation of the extremes of overidealization and devaluation. these people have difficulty tolerating being alone, and will make frantic efforts to avoid real or imagined abandonment.
affective instability is common. this may be evidenced by marked mood shifts from baseline mood to depression, irritability, or anxiety, usually last a few hours or, only rarely, more than a few days. in addition, these people often have inappropriately intense anger with frequent displays of temper or recurrent physical fights. they tend to be impulsive, particularly in activities that are potentially self-damaging, such as shopping sprees, psychoactive substance abuse, binge eating, reckless driving, casual sex, and shoplifting."
~ from the diagnostic and statistical manual of mental disorders, 3d edition, revised (1987), pp. 346-47