Being hyper-vigilant, Draco knew the moment someone walked up beside him, and a cursory glance informed him of the low threat the female posed, so his eyes had returned to the display. He was about to move away and inside to replenish his quidditch care supplies when the woman slipped. An instinctual reaction had him turned slightly, hand firmly placed upon her upper arm as he braced her to keep the woman from falling into the window.
Despite his actions to help stabilize her, he gave the woman a slightly bored and put-upon expression. Really, to be so clumsy as o fall while leaning. Was the woman drunk? No, he smelt no liquor on her, not that he would care one way or another. He released her arm once she was standing on her own feet again, stable.
"Do refrain from trying to fall through shop windows, I do not think they would enjoy the paperwork it would cause." His words were said in the same vein as his expression, and he moved to step away from the woman, whoever she was, dismissing her immediately as inconsequential.