Hey, fellow literary masochist here! I've looked over the Legendary Badfic on the Wiki, and I also think it needs some additions. While the ones they have are in fact absolutely horrific, I can tell the editors missed out on the darkness that plagued the net in my time (I.E late 90s). I'm surprised, frex, that the Marissa Picard Chronicles aren't on there. Others that definitely merit attention:
1.The Misery Sensei Neo-Zero Double Blitzkrieg Debacle. It's an epic length (500 page) Sailor Moon/Daria crossover that ends up being absolutely incomprehensible. Has been Msted, to great success.
2.The Oscarfics. Oh God. Written by a self-proclaimed 13 year old hermaphrodite, who inserts himself into the Sailor Moon Universe to pursue the affections of Artemis. That's right, the cat. Yeah. Some brave souls actually managed to MSTie it.
3. Agony in Pink. Quite possibly the worst Fanfic in existence. Completely blows My Immortal out of the Water. Basically, the Pink Ranger from Power Rangers gets kidnapped by the main villian and tortured, raped, and eventually murdered. So bad it actually caused Australia to ban Usenet for a while.

If anyone can so much as touch these, you will have my unending admiration and respect. Tread carefully.

If a story is so infamous that you can mention it's title and most people will groan and go, "oh, THAT one!", then it's Legendary. Same for goodfic - the list is (or, tries to be) only made up of stories that practically everyone has heard of.

That said, if something truly terrible comes up, we might just add it. Generally it's good to have consensus, though. I think it would be frowned upon to arbitrarily add a whole bunch of badfics to The List.