The Hive Mind said:
Title says it all. A friend keeps claiming Japan has the greatest culture in the world -- I need some really ripe, messed up anime as proof of how weird and creepy Japan can be.
I know they exist (all them 4chan-endorsed cat-girl fests 'n stuff) but I don't know the names of any of them so I can't just google them. Apparently
Regarding the phrase "messed up anime", not necessarily porn but I'd recommend Higurashi No Naku Koro Ni, and it's spiritual successor, Umineko No Naku Koro Ni. Those two are complete mindfucks, to the point that if they had been made in the West David Lynch would be the director. Also, Serial Experiments Lain has something of a reputation as being really screwy with your mind, though I haven't seen it myself to confirm this (want to though).
As far as anything perverted goes, there are plenty of anime that have prodigious amounts of fan-service in them, though they don't tend to be anything especially perverted or strange otherwise. An example would be Elfen Lied (which is actually pretty good anyway, though it does have a fair amount of gore and torture in it...). For proper perverted stuff, I won't list or link anything here because although this is the internet, there are still young people who visit this site and I don't want to get banhammered. However, I will tell you that you can find a long list of dozens, if not more, of hentai anime, games and manga on the TV Tropes page for Hentai. Just go to TV Tropes and if you can avoid branching off on different articles for hours on end, search for the Hentai page. There's a list there. Also, note that I take no responsibility if any young kids see this post and do the same, because frankly if they want to find the porn they'll be able to anyway. It is the internet, after all...
However, I have one more very important thing to say about your views on Japanese culture. It's true that some things coming out of Japan are weird and creepy. But first, you have to remember that their culture and way of life is somewhat different to that of the West. So things that appear odd to us may be perfectly normal in Japan. Second, and more importantly, a lot of the 'creepy and weird' stuff is actually denounced by the majority of the Japanese. The weird stuff is actually a very small minority of what Japanese culture is all about, and over there is akin to the existence of certain niche-market weird stuff in TV and film over here. If there's something you've seen here that's considered weird and creepy, then there's probably more than a 90% chance that it would also be considered weird and creepy by the vast majority and general public of Japan, and was created purely as a niche fetish thing or something. It's not a good idea at all to have such a narrow-minded view of Japanese culture, and you certainly shouldn't assume that everyone there follows anime and manga and supports tentacle porn and all that sort of stuff. Because that is simply a massive and damaging misconception...