I consider myself as having good taste, and have some friends with good taste, so yeah, if we're talking series (rather than movies) I've normally just not bothered with things that I know I'll hate. Which is unfortunately a lot more of recent anime, as I find the pedophilia of late anime utterly horrible. I mean, there's good bad and there's bad bad. What happened to adults being bloodily spattered everywhere with cursing? That was the good kind of badness which is watchable if sufficiently bored, as opposed to getting a shoe thrown at the screen and turned off. Le sigh. (And I'm not even a fan of the type of anime that had its previous bad reputation, but I'll take that any day over this. Random fun link you've probably seen before:
http://www.youtube.com/watch?v=bVpwJbLLivU& .)
For "worst anime series that I've successfully sat through in its entirety voluntarily..." hmm. I think I'm going to have to with Madlax here. I entirely disagree with saying Noir is bad, above (and for what it's worth, the flashbacks stop being so common after the 5th episode or so). However Madlax is all the lesser parts of Noir accentuated, the better parts of Noir removed, and some entirely ridiculous crap thrown in. The main reason I was able to sit through it was the lingering promise of resolving some of the more interesting mysteries from before, but said resolution was beyond lame anyway, so yeah. Great music, though, and some of the mysteries were presented well enough before hand. It's just that their resolution sucked. This show still isn't totally worthless, but I certainly can't recommend it.
The worst in general that I sensibly quit on... hmm, lots of options, and most of them say more about having misleading advertising than actually being bad. Again, I'm not going to bother even trying horrible harem shows. While I'm on a Bee Train rant, they haven't done anything right since Noir. .hack gets an A for idea and the first three episodes or so and then proceeds to inexplicably do absolutely nothing, not even good filler episodes. But even that's better than some of their other recent stuff. I gave Murder Princess a shot off of lingering respect for Noir and the general idea being salvageable. But the first episode alone has about ten head-desk worth moments. Yes, this show is more about putting women in fetish gear as quickly as possible, pretty much, while having a really horrid art design and style. Oh god did it suck horribly. That'll be my recent one-episode wonder to convince me not to watch.
On a slightly different note, for "worst anime that is still basically watchable and has some good points," I think I'll have to go with Gasaraki. It defines the exact line between mediocrity and bad; if it had been one iota worse, it'd be unwatchable. My college's anime club was showing it along with Key: The Metal Idol afterward, and Key was good enough that I didn't mind watching Gasaraki and ruthlessly mocking it with my friends. Gasaraki is one of those animes that has pretensions of being somewhat realistic, despite including giant robots. Fine. Except... it totally fails at being realistic, yet they clearly think they are, which is painful. The mystical plot is mildly interesting if not particularly creative, but their attempt at a political plot is pretty much Front Mission except hit in the head with a brick repeatedly (and Front Mission Political Plot is not really high on the scale). Sample story from it: Okay, there's one character who's basically read the script, i.e. he knows ridiculous things he shouldn't know and no one else should. This means that he knows three days early that the United States is going to have a press conference and declare to the world that their harvest was bad, and furthermore will probably ban exports & imports. This will lead to instability in Japan and knock out the government. Except... wait, no one else knows this three days before?! Did all the satellites blow up? Or for that matter tourists driving through Iowa? A famine is basically impossible to hide short of North Korea-esque restrictions on travel & communication. There wouldn't *need* to be a press conference that would surprise the world with this fact; everyone would already know if the weather was bad / a plague hit the crop / whatever. Furthermore, why on earth would the United States *close* their markets in event of a famine? The reason why poor countries sometimes do this is because they don't have money to buy outside food anyway, and asshole land barons may export some of the country's food for money anyway if the aristocracy is still fed. The United States is rich. We'd cheerfully keep markets open and buy other country's food, perhaps causing a famine in their countries. There's no incentive to close the markets whatsoever unless Japan is vastly more wealthy than the US in the future and also voraciously hungry! So yeah, this plotline fails. Apparently the director was under the sad deluded impression that having animated newsmen deliver the news made it realistic or something. Also, Gasaraki has among the worst opening episodes I've ever seen. Thankfully it recovers slightly, but the first episode? Watch it for the trainwreck. It's mostly about declaring completely ludicrous blood pressures (300 over 200? Yeah, your veins are now exploding) and then watching as technicians in the van inject compound C into the pilot. But oh no! Blood pressure still rising, let's try injecting Compound E!