This person is always smiling and saying superficially pleasant things, but there's a profound undercurrent of malice and spite just millimeters below the surface. Every single thing she says can be taken by a bystander as innocent, or at most, just a joke. She always retains plausible deniability against any complaint about her attitude or behavior, because each individual element of her constant, comprehensive, exhaustive campaign of malice is, taken by itself, so trivial and petty as to make the complainer look like a fool making mountains out of molehills. Yet collectively, if someone sticks around long enough to see it and makes even the slightest effort to pay attention, they accumulate into a vicious stream of self-centered belittlement and ridicule that speaks of a profound darkness of the soul.
Every word is sweet and soft, a perfumed silken caress, with a slender pointed dagger behind it. She cuts so cleanly you almost can't feel it at first. By the time you realize you're bleeding, she's flouncing away, and no one else would believe it, either.
She has a bevy of other ways to deflect criticism. One of her favorites is to put on airs of indignance at being judged. This one is especially popular if the objection is not to her, or her actions, but just their appropriateness to a particular situation. You're really trying to oppress her. Any criticism of anything she does or says is never actually what it says it is; it's simply a symptom of your personal, and irrational, dislike of her. She never actually answers any comment, criticism, or accusation. Never. She may respond, she will certainly speak afterwards, but she will never actually answer.
All of this should be of little import, because it seems like such an obvious ploy, such an obvious strategy. And such an easily recognizable pattern to anyone who looks for it for the tiniest amount of time. It oozes, after all, from everything she says. She thinks she's very very clever to have invented it; she's positively smug, smirking all the time. You want to laugh at her for being so proud of inventing something so obvious and so recognizable.
But... somehow, almost everyone doesn't recognize it. Doesn't realize it. Falls prey to it, over and over. So much so, that anyone who does recognize it and tries to say something gets not only ignored but marginalized. They get seen as the troublemaker for complaining about such petty matters, in the eyes of all the people who fall for it.
I wish there were a nice simple name you could use for this kind of person. Something along the lines of "passive-aggressive" or "anal-retentive", something that sums up the whole pattern of behavior and thus makes it more readily recognizable. But if there is one, I don't know what it is. But most of all I wish more people would learn to recognize this pattern. It's depressing that such a simple and obvious tactic works so darned well.