i think that the majority of people who meet criteria for BPD meet criteria for one or even two other personality disorders as well. typically avoidant or narcissistic. sometimes anti-social. some people have tried to explain that the reason more women are diagnosed with BPD is because guys tend to act out, go to jail, and end up with a dx of anti-social instead.

i think the main difference between borderline and avoidant is that most people with BPD are more on the dramatic side. actively seeking proximity with people. but then you get the inhibited emotional expression variety and i guess that tends to be correlated with avoidant. avoiding proximity with people.

not sure that there is a hard and fast line

officially (apologies in advance for the judgemental crap)

Other Personality Disorders may be confused with Borderline Personality Disorder because they have certain features in common. It is, therefore, important to distinguish among these disorders based on differences in their characteristic features. However, if an individual has personality features that meet criteria for one or more Personality Disorders in addition to Borderline Personality Disorder, all can be diagnosed. Although Histrionic Personality Disorder can also be characterized by attention seeking, manipulative behavior, and rapidly shifting emotions, Borderline Personality Disorder is distinguished by self-destructiveness, angry disruptions in close relationships, and chronic feelings of deep emptiness and loneliness. Paranoid ideas or illusions may be present in both Borderline Personality Disorder and Schizotypal Personality Disorder, but these symptoms are more transient, interpersonally reactive, and responsive to external structuring in Borderline Personality Disorder. Although Paranoid Personality Disorder and Narcissistic Personality Disorder may also be characterized by an angry reaction to minor stimuli, the relative stability of self-image as well as the relative lack of self-destructiveness, impulsivity, and abandonment concerns distinguish these disorders from Borderline Personality Disorder. Although Antisocial Personality Disorder and Borderline Personality Disorder are both characterized by manipulative behavior, individuals with Antisocial Personality Disorder are manipulative to gain profit, power, or some other material gratification, whereas the goal in Borderline Personality Disorder is directed more toward gaining the concern of caretakers. Both Dependent Personality Disorder and Borderline Personality Disorder are characterized by fear of abandonment, however, the individual with Borderline Personality Disorder reacts to abandonment with feelings of emotional emptiness, rage, and demands, whereas the individual with Dependent Personality Disorder reacts with increasing appeasement and submissiveness and urgently seeks a replacement relationship to provide caregiving and support. Borderline Personality Disorder can further be distinguished from Dependent Personality Disorder by the typical pattern of unstable and intense relationships.

Borderline Personality Disorder must be distinguished from Personality Change Due to a General Medical Condition, in which the traits emerge due to the direct effects of a general medical condition on the central nervous system. It must also be distinguished from symptoms that may develop in association with chronic substance use (e.g., Cocaine-Related Disorder Not Otherwise Specified).

Borderline Personality Disorder should be distinguished from Identity Problem...which is reserved for identity concerns related to a developmental phase (e.g., adolescence) and does not qualify as a mental disorder."