Short, creepy fic

[dawnriots]

Google comes up with nothing, but perhaps the community here knows. There's a short fic, decidedly NC-17, under 500 words, that's somewhere on LJ. Harry's sitting in his dorm (?) and jerking off and he keeps fantazising about Snape chasing him through the dungeons, wearing the Death Eater robe and mask. Just as Snape catches him, yanking and pretty much breaking his arm, Harry ends up coming in his hand.

Does anyone know this piece? It's haunting... and lost. Can't find it. Help!