If you think of the Cluster B (“dramatic”) disorders (characterized by either too much emotion or the masking of true emotions) as malfunctions or problems of the sufferer’s “emotional thermostat,” their differences make more sense. The emotional thermostat determines how a person handles their own emotions or reacts to those of others.
Borderline Personality Disorder (BPD): inability to regulate emotions (a thermostat that works but is having problems–cutting on the heat or air when it isn’t needed or shutting it off when it is, but half the time works perfectly). This explains their ambivalence in relationships (“I hate you…don’t leave me,” “go away, come closer.”)
Histrionic Personality Disorder (HPD): inability to control emotions (a thermostat that is always on High and blasting heat even when it’s already too hot). That’s why they overreact to everything.
Narcissistic Personality Disorder (NPD): inability to access true emotions (a thermostat that sets to “cold” and turns on the air conditioner when heat is needed, and “hot” and turns on the heat when the air conditioning needs to be on). This explains their lack of empathy and show of fake emotions that may not fit a given situation.
Antisocial Personality Disorder (AsPD–psychopathy, sociopathy): total inability to empathize or respect the rights of others (a broken thermostat that doesn’t work at all.) People with ASPD are unable to feel any emotions except rage.