Fandom Inquiry: The Most Disturbing Fic in Fandom

I'm rather curious to know what's considered the 'Most Disturbing Fic in Fandom.'

By 'disturbing' I mean a number of things;

Sexually
Mentally
Physically
Visually

Do the words 'macabre', 'nightmarish', and just plain 'fucked up' come to mind?

Does Snape make Captain Howdy look like Mother Theresa?

Did you have nightmares over Draco in a pink tutu carrying a ukelele?

Does the thought of Filch graverobbing and corpse fucking make you want to spork out your eyes with white hot sewing needles?

Basically, I want to know what fic made you say;

Goddamn! Now that was some fucked up shit! I don't think I'll be able to sleep tonight!

Please leave links. I might compile a list :-)

--P