The pathological personality of a narcissist manifests itself in his pretense of not caring for someone, particularly a person who ceases to be an instrument of the narcissist's self-gratification.
Behind the pretense is the desire to woo his "source of supply" back to being his enabler in narcissism. The narcissist therefore erects a facade of indifference by giving the erstwhile enabler the silent treatment, for example. By pretending to devalue and discard the enabler, he secretly hopes to draw him back into his web of self-centeredness. The former enabler, if sufficiently perceptive, will recognize the feigned indifference for what it really is: a mask that hides the narcissist's aggression and hostility for having been "dumped."
In the war between the sexes, the ploy of a woman, for example, who pretends not to be interested in a man when in fact she is highly attracted to him, is quite common, and while there is a touch of narcissism in that particular ploy, it can also lead to a mutually satisfying relationship of give and take, and not just the one-sided take, take, take of the narcissist and his enabler.
We should also not ignore the obvious: for there to be irony, there also needs to be an ironist (at least in non-situational ironies). In ancient Greek plays, one of the stock characters was the eiron who pretended to know less than he actually did. His foil was the alazon who pretended to know much more than he actually did. The eiron, much to the delight of the audience, exposed the ignorance and hubris of the alazon by sucking him into his web of intrigue with subtle and not-so-subtle enticements of feigned ignorance, as if to say, "Oh, please, do enlighten me!"
Finally, in child-rearing, the wise parent might feign indifference when the child threatens to run away from home. The parent will say, "OK, I'll help you pack a suitcase!" When the child senses the parent will not miss him, and that he's actually going to be away from home and on his own, he starts to have second thoughts. A case of simple psychology. Is there a name for the parent in this case? Well, ironist comes to mind!