Okay, I admit, the title totally made me click on this. Well, that, and the fact it said "extremely NC-17" and I just had to see what made something extremely. *smirk*
(Are you buying that? I didn't think so.)
But in all seriousness, here's what I wanted to say about this: in just over 2,000 words, you have somehow managed to convey that thing that is so elusive and slippery that it really can't be captured well with words; something I don't think I've ever read before in a fic, or at least not quite like this. That "something" is the feeling of being so desperately, ridiculously, hopelessly aroused that you are past caring what is even happening to you, you Just. Need. To. Fuck.
GAH.
I love that you went there, that you made it so palpable I could feel the scene, not just watch it. Yes, the smut was delicious, but what you did with the writing and the way that you showed it was even better.
And for some reason, I was touched by the fact Harry stole Severus' robes. I don't know why such a small gesture should mean so much, but it did.