Check out borderline personality disorder. It shares a lot of characteristics with narcissistic personality disorder. One thing that leads me to this over other disorders, which may also be present, is the 'empty vessel' and 'role-playing' displayed by those who suffer. In essence, they have no personality of their own and take on roles that they play until they tire of them, like KC took on the role of mother for a while. Chameleon is a good descriptor because having nothing of their own to offer, they often take on the role of and appear to be like those with whom they associate. Remember how KC changed after hanging with JB a while? A good book on personality disorders that's been around forever is, "I Hate You - Don't Leave Me." The title alone suggests part of the pathology. Here are a few links and some quotes from the latter:
http://www.nimh.nih.gov/health/publications/borderline-personality-disorder-fact-sheet/index.shtml
or
http://www.fortunecity.com/campus/psychology/781/bpd-dsm.htm
"...Individuals with Borderline Personality Disorder have a pattern of unstable and intense relationships (Criterion 2). They may idealize potential caregivers or lovers at the first or second meeting, demand to spend a lot of time together, and share the most intimate details early in a relationship. However, they may switch quickly from idealizing other people to devaluing them, feeling that the other person does not care enough, does not give enough, is not "there" enough. These individuals can empathize with and nurture other people, but only with the expectation that the other person will "be there" in return to meet their own needs on demand. These individuals are prone to sudden and dramatic shifts in their view of others, who may alternately be seen as beneficent supports or as cruelly punitive..."
"...There may be an identity disturbance characterized by markedly and persistently unstable self-image or sense of self (Criterion 3). There are sudden and dramatic shifts in self-image, characterized by shifting goals, values, and vocational aspirations. There may be sudden changes in opinions and plans about career, sexual identity, values, and types of friends..."
"...The basic dysphoric mood of those with Borderline Personality Disorder is often disrupted by periods of anger, panic, or despair and is rarely relieved by periods of well-being or satisfaction.
These episodes may reflect the individuals extreme reactivity troubled by chronic feelings of emptiness (Criterion 7). Easily bored, they may constantly seek something to do. Individuals with Borderline Personality Disorder frequently express inappropriate, intense anger or have difficulty controlling their anger (Criterion 8). They may display extreme sarcasm, enduring bitterness, or verbal outbursts. The anger is often elicited when a caregiver or lover is seen as neglectful, withholding, uncaring, or abandoning..."