Disclaimer: JKR owns the Harry Potter world - I just like to play around in it.
A/N: Mild HBP Spoilers - you've been warned!
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Severus Snape sat on his four-poster bed in the Slytherin fifth-year dormitory. Round-shouldered and sunken-chested, he gave off the impression of someone trying to disappear into their surroundings. His stringy black hair was falling in his face as he scribbled notes in an old, battered textbook. He lifted his head and brought his hand to his face, tracing his lower lip. With a sudden inspiration, the fifteen year-old boy picked up his wand and aimed it at his bare foot.
"So, if I try 'secuisempra', I get . . . ouch!" A large blood blister appeared on the arch of his left foot. With a singsong voice, he muttered a countercurse that he hoped would work. The blood blister drained away and disappeared. Ok, well that one's not very impressive, he thought to himself. You know, if I do manage this one – perhaps I should try it out first on that damn Mrs. Norris instead. He laughed at the thought, but then reconsidered. Mrs. Norris was a hateful pile of matted fur, but that old squib wasn't so bad. He at least hates them almost as much as I do.
Just then, the dormitory room door banged open and two Slytherin students stormed in. One was a tall brown-haired boy with a large, sloping forehead, the other a rather squat curly-haired boy with no chin and even less neck. His head seemed to just sit on his shoulders like some kind of loose pebble on a board. It didn't help that he seemed to wiggle and shake it constantly as he spoke.
"I just need my DADA notes so I can go over them one more time before the written exam tomorrow afternoon" said the brown-haired boy to his Weebel-like friend. As the boy looked over at Severus, a mild look of disgust crossed his face.
"Ever wash your hair, Snape, you soap-dodger?" he asked.
"Sod off, Wilson!" replied Severus with venom. The curly-haired boy giggled so fiercely, Severus thought his head might roll off.
"Oooh! You told him, didn't ya, Snivellous."
Severus' already pale face blanched further. He stood up, whipped out his wand and pointed it at the little Weebel.
"Say that again, McCormick and see what happens!" he hissed.
"Now, now," said Wilson, eyeing the wand with a little unease, "He was just taking the mickey out of you." Severus lowered his wand, but kept it in his hand. Wilson looked him up and down and added, "You know – letting those Griffies have a go at you all the time makes us all look bad. Better get a handle on them." With those sage words of advice given, Wilson grabbed his notes, and he and McCormick headed out the door.
'Let them have a go? Let them?' Severus fumed silently to himself. As if he'd ever taken it lying down. He'd never taken anything from them, and never would. Four on one – it was always four on one! If he could just once get one of them alone! Then they'd see, then they'd realize just who they were dealing with. Severus sat back down upon his bed and picked up his quill and book again.
He could feel the hatred boiling up inside of him. He liked this feeling, it was powerful, it was real; It helped him focus his thoughts. Once he had his new spell figured out, he would have the power. Then they would be sorry.
He found a blank spot on the top of one of the pages and wrote 'For Enemies'. Once he had perfected his spell, that's where he would put it. A glint in his eye, Severus picked up his wand again. 'For my enemies' he thought to himself.