Potter's gaze falls unerringly on the box, eyes widening a little, and Draco mentally snarls that drunkards ought to at least attempt a little less awareness of their surroundings in order to preserve the image. But Draco won't let himself resent Potter's neuroses because they have saved his life more times than he cares to recount.
Potter meets his eyes and immediately says, "You're an idiot, Malfoy," and takes a seat on one of the heavy mahogany chairs on the opposite side of his desk. His words are slow and a bit slurred, and if the straggly beginnings of a beard on his face are anything to go by, he has not done anything but indulge in days. His bitter, alcoholic smell supports the theory.
Draco had long ago decided that tact was not one of the Good Guys' defining characteristics. Ron Weasley certainly taught him that much (though he'd always had vaguely higher standards for Potter, but then, hadn't everyone?). However, this does not excuse a similar lack of common decency and politeness in Draco himself until further into the conversation and the bottle of scotch. He settles for raising an eyebrow and saying, "Excuse me?" the same way he would say, "Please fuck off, you prat."
Potter's words are too slow, carefully shaped in his mouth before they are uttered to keep from slurring them, but his intent is perfectly clear. "You're really going to. Malfoy, you're an idiot. There is idiotic, and then there is this."
Draco does not know what the generally accepted response to this speech is. All that he knows is that he's not terribly interested in sitting here with his arch nemesis turned cautious ally turned jaded drinking partner and listening to why he, Draco Malfoy, owner of Malfoy Magical Potions, Ltd., the second wealthiest individual in England after that muggle Queen, latest in a long a glorious line of Malfoy heirs, should listen to the Boy-Who-Lived-To-Become-A-Has-Been for life advice. He tries and fails to remember the last time he or anyone else saw Potter outside of Malfoy Manor, Harry's dismal excuse for a flat, that horrible pub Harry insists on frequenting, or a Hogswart reunion.
"Did anyone say I had any intension of using it?" he asks. His tone clearly states, "Shut the hell up." He's very successful at channeling it on most occasions, and it has been known to make four research assistants, two clerks, and, in a rather memorable moment, one Daily Prophet photographer cry.
Unfortunately, Potter has faced down Lord Voldemort, and it seems one Draco Malfoy holds little terror for him. He gives Draco his patented I-am-Harry-Potter-and-I-can-assure-you-that-you-don't-want-to-do-this stare, which would be more effective if he hadn't been swaying while seated in his chair.