Here are the criteria for the 4 Cluster B personality disorders taken from the DSM - IV - TR:

Borderline Personality Disorder

A pervasive pattern of instability of interpersonal relationships, selfimage,
and affects, and marked impulsivity beginning by early
adulthood and present in a variety of contexts, as indicated by five
(or more) of the following:

1. frantic efforts to avoid real or imagined abandonment. Note:
Do not include suicidal or self-mutilating behavior covered in
Criterion 5.
2. a pattern of unstable and intense interpersonal relationships
characterized by alternating between extremes of idealization
and devaluation
3. identity disturbance: markedly and persistently unstable selfimage
or sense of self
4. impulsivity in at least two areas that are potentially selfdamaging
(e.g., spending, sex, substance abuse, reckless driving,
binge eating)
5. recurrent suicidal behavior, gestures, or threats, or selfmutilating
behavior
6. affective instability due to a marked reactivity of mood (e.g., intense
episodic dysphoria, irritability, or anxiety usually lasting a
few hours and only rarely more than a few days)
7. chronic feelings of emptiness
8. inappropriate, intense anger or difficulty controlling anger
(e.g., frequent displays of temper, constant anger, recurrent
physical fights)
9. transient, stress-related paranoid ideation or severe dissociative
symptoms

Histrionic Personality Disorder

A pervasive pattern of excessive emotionality and attention seeking,
beginning by early adulthood and present in a variety of contexts,
as indicated by five (or more) of the following:
1. is uncomfortable in situations in which he or she is not the center
of attention
2. interaction with others is often characterized by inappropriate
sexually seductive or provocative behavior
3. displays rapidly shifting and shallow expression of emotions
4. consistently uses physical appearance to draw attention to self
5. has a style of speech that is excessively impressionistic and lacking
in detail
6. shows self-dramatization, theatricality, and exaggerated expression
of emotion
7. is suggestible (i.e., easily influenced by others or circumstances)

Narcissistic Personality Disorder

A pervasive pattern of grandiosity (in fantasy or behavior), need for
admiration, and lack of empathy, beginning by early adulthood
and present in a variety of contexts, as indicated by five (or more)
of the following:
1. has a grandiose sense of self-importance (e.g., exaggerates
achievements and talents, expects to be recognized as superior
without commensurate achievements)
2. is preoccupied with fantasies of unlimited success, power, brilliance,
beauty, or ideal love
3. believes that he or she is “special” and unique and can only be
understood by, or should associate with, other special or highstatus
people (or institutions)
4. requires excessive admiration
5. has a sense of entitlement (i.e., unreasonable expectations of
especially favorable treatment or automatic compliance with
his or her expectations)
6. is interpersonally exploitative (i.e., takes advantage of others to
achieve his or her own ends)
7. lacks empathy: is unwilling to recognize or identify with the
feelings and needs of others
8. is often envious of others or believes that others are envious of
him or her
9. shows arrogant, haughty behaviors or attitudes

Antisocial Personality Disorder

There is a pervasive pattern of disregard for and violation of the
rights of others occurring since age 15 years, as indicated by three
(or more) of the following:
1. failure to conform to social norms with respect to lawful behaviors
as indicated by repeatedly performing acts that are
grounds for arrest
2. deceitfulness, as indicated by repeated lying, use of aliases, or
conning others for personal profit or pleasure
3. impulsivity or failure to plan ahead
4. irritability and aggressiveness, as indicated by repeated physical
fights or assaults
5. reckless disregard for safety of self or others
6. consistent irresponsibility, as indicated by repeated failure to
sustain consistent work behavior or honor financial obligations
7. lack of remorse, as indicated by being indifferent to or rationalizing
having hurt, mistreated, or stolen from another

Psychopaths fall under the antisocial heading. Clinically, some people use the terms sociopath and psychopath as an indication of how bad the disorder is, sociopath being the lesser of the two and psychopath being the worst.

If the personality disorder is bad enough, Cluster B's will often show partial or considerable overlap into other areas. For example, my ex showed traits and behaviors from the Narcissistic, Histrionic and Borderline Personality groups.

Every one of us have at least a small amount of narcissistic tendencies within us, but full-blown narcissists notch those behaviors and traits way over the top.