Severus Snape fairly ran back to the castle, his bunched-up underpants chafing uncomfortably between his legs, his pallid cheeks still burning with anger and humiliation. Bloody Potter, he thought, angrily swiping his oily hair away from his face with the back of his hand.
No one in the common room even glanced at him as he entered. The news of his humiliation by the Gryffindor gang had evidently not yet reached the few who were spending the afternoon indoors; Not that his social status could fall any lower in their eyes. He was, after all, a half-blood: an ugly, greasy, unsociable type whose only friend was (had been) a Gryffindor mudblood. He wasn't worth their time – he had no connections to cultivate.
Maybe now, with Evans no longer speaking to him, he could stop wasting his secrets on her, and show them what he was really capable of. There were a few spells he had been pondering lately that Avery and Mulciber might appreciate. Maybe they would grow to think of him as more than just a goon?
Carefully opening the door to the dormitory, and glancing in front and in back to make sure there was no one there, he walked jerkily over to his bed, and sank down on it. A crackling sound issued from under and behind him, and he shifted to see what he had sat down on.
It was a thin parcel, not much larger in area than a textbook, but soft and flexible, wrapped in non-descript brown paper. Attached was a note, written in thick flourishes on heavy parchment:
Severus:
To make a good impression, it is what is on the inside that matters.
H.E.F.S.
Wincing at the triteness of the sentiment, Snape stood up, and undid the wrapping in the parcel with his wand from a distance. The paper fell away easily, and stepping closer, Snape poked at the contents. Hooking the tip of his wand in the centre, he lifted up what seemed to a mass of glossy fabric. Held this way, the folds revealed themselves to be a pair of silk shorts, in the darkest black with a pattern of snakes slithering slowly over the surface.
Slughorn had just sent him new underwear. Frowning at the shame of knowing his Head of House had witnessed his helplessness before Potter's hexes, he snatched the shorts violently off his wand. But the soft silk rustled seductively in his fist, and Evans' taunting words came back to him: "I'd wash your pants if I were you, Snivellus."
From force of habit formed over five years of living at the school, Snape rushed into a large wardrobe to change. There, in the dark and solitude, his movements stifled by the robes and Quidditch uniforms crowding the space within, he clumsily shoved his graying, bunching, stretched-out, pilled, Yorkshire underpants down his legs, and off his ankles. Straightening the waistband of the new silk shorts, he slipped them up his skinny legs, and onto his bony hips. They felt warm, yet cool as they settled beneath his released robes, as though they had been there all along.
Stepping out from the wardrobe, he kicked his discarded underwear onto the stone floor. Pointing his wand at it, he shouted, "Incendio!" The grey cotton curled and twisted beneath the flames, dissolving easily into smoke and cinders. "Evanesco," Snape whispered at the remains of his past.
Walking out of the dormitory, his spine straight, and his robes billowing behind him like black wings, Snape held his wand in his hand, now ready to prove his powers.