Severus and his body had been at odds for years. The Christmas that Dumbledore pulled out all the stops and let students order whatever they wanted, Severus simply stared at his golden plate. He was unsure of his favorite food or even what he was hungry for at the moment. And he couldn't remember ever knowing.
At the Gryffindor table, Black tore into a turkey leg. Suddenly a working relationship with one's tongue and stomach seemed very Gryffindor. Severus wondered spitefully if the git's parents had kept him here because they didn't want to see him eat.
Slughorn once recommended Lily a potions book from the Restricted Section. When she finished it, Severus had his turn. He could barely take his eyes off it: reading it in classes, reading it late at night. When he had a few hours after class, he luxuriated in it. Once, he looked at the alarm clock with a jolt; he missed dinner by an hour. But he'd missed meals before. Thus began a pattern; he'd sporadically forget meals, lost in study, and became a little sulky until the next scheduled mealtime.
Severus took short, awkward showers. He didn't particularly like his nakedness—white as a cave-blind fish, he'd think sometimes, not to be outdone by James even at insulting himself. He knew he had poor dress-sense and worse hygiene. No one would let him forget it. But he dreaded even more than his ugliness the humiliation of trying, and failing.
Imagine what Black would say: "An almost-decent job washing your hair, T for trying! But the nose, Snivvy. And the face. And the body? A little effort on those bits. Not that I could imagine anything helping."
Severus stayed up too late because he rarely liked his dreams.
Severus decidedly didn't like his body. It was demanding, and frustrating, and took away from his time to think and to read and to practice magic. He had ignored it so long he couldn't really tell what it wanted anymore.
Except for one, very particular want.
It could be sharp and unexpected, like that time she surprised him in the library with her hands over his eyes; he'd stiffened and fallen out of his seat. Or an impossibly long heart-pause, like when they read together and he could watch her for whole minutes. It could be pure freshness, aching like a sudden April when she did something that was simply so Lily. And since thirteen he had known that his body somehow held the culmination and exaltation of these feelings. All he had to do was touch.
Got a dick and a mind greasier than your hair, Severus told himself.
Author's note: the idea is that when Tobias started beating him, Severus pretty much shut down his bodily awareness so that he wouldn't feel it as much, and started denigrating his body so the beatings would seem unimportant. Knowing that he did grow up in an abusive household, this kind of body seems like a pretty good explanation for his greasy hair and part of the awful temper (so many mood problems are related to not meeting physical needs).
His physical need for Lily is different, because it shows up later in his life than beating and eating, which probably started at about the same time.
But Severus isn't self-aware enough, at least physically, to realize all this, and since this story is in his point of view I have to give you this fucking cheaply-written author's note. I WANT TO SHOW AND NOT TELL