(The following post talks about The Avengers on its way to the actual point, but does not give spoilers.)
Interestingly, one of the moments that has stayed with me the most strongly from The Avengers is the speech Loki flings at Black Widow.
He has other Villain Speeches in the movie, of course. But this one stands out for its sheer, unbridled malevolence. He doesn't say those things out of megalomania or fraternal resentment or any other such understandable motivation; he says them because, quite simply, he wants to hurt her.
I've said before that I tend to write antagonists more often than villains. That is, I write characters who think they're doing the right (or at least the necessary) thing, who happen to be wrong about that. There are exceptions, of course; Nadrett doesn't give a damn what's right, only what he can get away with. But I have a harder time writing that sort of thing.
Which means -- of course -- that I want to study how it's done. So this is a Recommend Stuff to Me kind of post: what books/movies/TV shows/etc have those moments of pure malevolence, where the character is just trying to hurt somebody? Off the top of my head, there's Dunnett's Lymond Chronicles ("Stop sidling, my swan. I am going to hurt you, but I am not going to kill you, just yet. You are going to provide me with a deal of merriment still."), some of Angelus' moments in Buffy, and pretty much everything the main villains do in Tokyo Babylon and X, but I'm having trouble thinking of more. (Actually, that's a lie. I can think of plenty of sadistic villains. It's just that most of them are sadistic in a shallow, uninteresting way, and I want ones that really manage to get the knife between the ribs.)
Where have you seen this done well?
Edited to add: Please to be avoiding spoilers as much as possible. This discussion will necessarily involve a degree of revelation, but if you can use phrases like "the main villain" instead of the name (where the villain is not obvious from the start), etc, that would be much appreciated.