They start by increasingly deriding any subject or interest the victim feels good about. If the victim likes intimacy and sex, they will deny them both, leaving the victim feeling dependent on their abuser's whims to occasionally allow it. If they can not answer an obvious question about their abusive behaviour, they will use the "Silent Treatment", meaning (quite simply), that they will obstinately refuse to say anything, leaving their victim feeling helpless, and alone.
They will never show these traits to other people, as they desperately need Narcissistic Supply. They search for this supply in any situation, and are bitterly frustrated when it is not forthcoming. An NPD is always in a state of fluctuation between depression and the constant search for Narcissistic Supply.
Ken Heilbrunn MD, about Malignant Self-love: Narcissism Revisited: [Abbreivated]
NPD: "First I build you up, because that's what you need. Your skies are blue. Then I start tearing you down. You let me do it because that's what you are used to.
You are incompetent, disrespectful, untrustworthy, immoral, ignorant, inept, egotistical, constrained, and disgusting. You are a social embarrassment, an unappreciative partner, an inadequate parent, a disappointment, a sexual flop, and a financial liability. I tell you this to your face. It is my right. I will behave anyway I want to, with total disregard for conventions or the feelings of others. It is my right, because it is.
I lie to your face, and there is absolutely nothing you can do about it. In fact, my lies are not lies at all. They are the truth; my truth. And you believe them, because they do not sound or feel like lies. To do otherwise would make you question your own sanity, which you have a tendency to do anyway, because from the very beginning of our relationship you placed your trust and hopes in me, derived your energy from me; gave me power over you."