Harry using Tom's diary to tease and write smutty passages about all the sordid playful things he'd like to do to Draco.
"Dear Tom, today Draco looked so fetching in potions class, I couldn't take my eyes off him...,"
"Dear Tom, Draco stopped me on the way to Herbology this morning.. let's just say we took a detour through the Forbidden Forest instead, we snogged for a good hour on the back of a thestral, it was wicked.."
"Dear Tom, Draco and I do it everywhere now, buck naked, the astronomy tower, Hagrid's hut, while he's still in there, Dumbledore's desk, all we need is my invisibility cloak and a silencing charm and it's a piece of cake..."
"Harry, this diary is a horcrux. Kill it."