Well, while 4chan isn't as bad as those who've never been on it say, most of it is still stupid, pointlessly offensive, and just generally mentally deficient. I was on there for 2 weeks, nearly turned me off the internet.
Then I discovered this place! Yay!
I think the worse places on the internet are probably white supremacist websites. I was reporting one of them (a joint venture between British skinhead group Combat 18 and Northern Irish paramilitaries the UDA) to some sort of internet regulatory committee and looking at some of it, it really truly showed how perverted the human psyche can become. Seriously, if you ever meet one of these people online, never entertain them by being offended by what they say, just ignore them because they are all, without deviation, pathetic, uneducated and small minded bigots.