Four Letter Words by weatherby
This one starts off like this: It only takes two hours for most of the sixth year boys to find out that Draco Malfoy has a pornographic novel on him, and at lunch the Slytherin table is crowded with a cluster of boys from every house pestering him to let them see.
If that's not enough of a reason to read it, I don't know what is. Oh, and it's TEH HOT, too. :D