I don't have the same "how could you feel this way?" reaction to it that Anke expresses, so I was pretty sure I must have felt this way about some villain at some point. But it took me a while to think of an actual example. Some counter-examples:
DC's the Joker: I don't love to hate the Joker. I just hate him and wish Batman (or anyone) would kill him. Lut was talking about watching the intro to one of the Batman video games, where Batman is escorting the Joker back to the asylum and the Joker is apologizing for not killing more people on his way out the last time and gloating about how many more he'll kill during the next escape. Me: "And the game doesn't let you kill the Joker here." Lut: "NO." Me: "See, this is why I wouldn't want to play it." Lut: "Y'know, if I were one of those armed guards standing around while the Joker was brought in AGAIN, I'd shoot him dead. And then I'd hand Batman my gun and say 'You can arrest me if you want to. But the only two people who are going to be sorry that bastard is dead are you and Harley Quinn. AND I'M NOT SO SURE ABOUT HARLEY.'" That would be AWESOME. Anyway, I know a lot of people like seeing the Joker vs Batman conflict play out again and again, but I am not one of them.
Marvel's Magneto: I don't love to hate Magneto either, but unlike the Joker, my response to Magneto is generally BE GOOD ALREADY DAMMIT. I like Erik and I want him to do good things and stop being so Machiavellian. I don't want him to be an unforgivable murderer. I sympathize with him, but I don't like watching him be a villain.
I can readily think of other characters that fall into one of those two camps: unsympathetic villains that I hate, and sympathetic ones that I want to see reformed. But coming up with a villain that I enjoy as-a-villain is much harder. The one I did produce is an actual classic:
Shakespeare's Iago: No, not Disney's snarky parrot, but the antagonist of "Othello". Iago is throughly villainous and almost completely unsympathetic, but he is very good at being a villain. It's been a long time since I read "Othello" and I've never seen it performed, but here's how I remember the play's structure: Iago comes on stage, gives a soliloquy listing his resentments and desires, and then explains how he's going to manipulate everyone in the next few scenes into doing what he wants them to. In the next few scenes, Iago uses a masterful combination of fabrications and apparent empathy and feigned good intentions to get everyone to do their part, most of them unwittingly, in his plan. Repeat until end of play. I cannot like him, or root for him, but there's a certain admiration for how well he executes his plot.
I am not sure that's the same emotion that most people associate with the phrase "villains you love to hate", but I think it's as close as I come. It's a hard category to get into, because it requires the character to be an unsympathetic, unapologetic villain, and yet have enough class/style/brilliance to make them entertaining despite that. And of course, it's subjective -- I'm sure there are people who feel that way about the Joker, or Moriarity, or Loki*, but I don't. So I'm curious -- what villains make the cut for you?
* Loki (in both the Norse myths and the recent films, oddly) is more in the want-to-see-reformed camp , although the end scene of Thor 2 was pretty awesome. Moriarity, I just hate.