The American Psychiatric Association provides a concise definition of personality disorder, but they are explicitly measuring the defect if you will against culture’s standards.
A personality disorder is a way of thinking, feeling and behaving that deviates from the expectations of the culture, causes distress or problems functioning, and lasts over time.
The DSM-5, which is a reference for psychologists and psychiatrists for diagnosing disorders, organizes it in terms of personality functioning and the presence of pathological traits and defines it as follows.
The essential features of a personality disorder are impairments in personality (self and interpersonal) functioning and the presence of pathological personality traits. To diagnose a personality disorder, the following criteria must be met:
- Significant impairments in self (identity or self-direction) and interpersonal (empathy or intimacy) functioning.
- One or more pathological personality trait domains or trait facets.
- The impairments in personality functioning and the individual‟s personality trait expression are relatively stable across time and consistent across situations.
- The impairments in personality functioning and the individual‟s personality trait expression are not better understood as normative for the individual‟s developmental stage or socio-cultural environment.
- The impairments in personality functioning and the individual‟s personality trait expression are not solely due to the direct physiological effects of a substance (e.g., a drug of abuse, medication) or a general medical condition (e.g., severe head trauma).
So it’s best and most accurate to say that a personality disorder is one that has the features of impairments in personality as well as having the presence of pathological personality traits. Well, I usually think of the word pathological as meaning something that just doesn’t work for the situation at hand and is often extreme. Let’s see what the DSM says about this.
characterized by adaptive inflexibility, vicious cycles of maladaptive behavior, and emotional instability under stress.
To define pathological correctly, it looks like it must have the features of not being able to be appropriate or adequate for the situation along with possessing an unstable pattern of it, especially when under stressors.
DSM-5 and Clusters
If you look at how the DSM organizes the ten personality disorders, then you’ll notice that they use key features to put them in groups called clusters. The group that is of interest to us is cluster B, Figure 1 below, which uses the characterization of dramatic and erratic behavior to describe the four disorders: BPD, HPD, ASPD, and NPD.
This behavior described seems to be similar to impulsiveness which means having little control over behavior and emotions, but phrasing the behavior as dramatic and erratic seems to add nuances while avoiding unwanted connotations.
Those that show subclinical symptoms of Machiavellianism, narcissism, and psychopathy may also benefit from reading this cluster, see the text in bold since it describes the bold element to their behavior remarkably well.
The “Cluster B” personality disorders are characterized by dramatic or erratic behavior. People who have a personality disorder from this cluster tend to either experience very intense emotions or engage in extremely impulsive, theatrical, promiscuous, or law-breaking behaviors.
- Borderline Personality Disorder (BPD) is characterized by emotional instability, intense interpersonal relationships, and impulsive behaviors.
- Histrionic Personality Disorder (HPD) features a need to always be the center of attention that often leads to socially inappropriate behavior in order to get attention. People with this disorder may have frequent mood swings as well.
- Antisocial Personality Disorder (ASPD) tends to show up in childhood, unlike most other personality disorders that don’t appear until adolescence or young adulthood. Symptoms include a disregard for rules and social norms and a lack of empathy for other people. [This “umbrella” term of Antisocial Personality Disorder includes the traits of sociopathy and psychopathy.]
- Narcissistic Personality Disorder (NPD) is associated with self-centeredness, exaggerated self-image, and lack of empathy for others.
 Salters-Pedneault, Kristalyn, Ph.D. Introduction to the DSM Personality Disorders. https://www.verywellmind.com/personality-disorders-a2-425427