Severus Snape considers himself an effective teacher. He is not kind - he cannot afford to be. He must have strict, absolute control of his classroom and the children under his care, lest they make a careless mistake and cost lives.
He also, of course, enjoys watching them cower when he sets his black eyes on them, watching them scurry to get out of his way as he strides confidently down the corridors after classes and at the weekend.
Severus Snape is not a nice man, and he makes no effort to hide this fact.
Being nice gets you killed.
Being nice gets others killed, too, though Severus would never admit to caring about that.
Being nice, in short, is not an intelligent or effective way to live. Especially for Severus.
Severus Snape considers himself a tolerant man, because the things he is willing to tolerate are many.
He tolerates the low, constant, throbbing pain in his arm.
He tolerates Albus' annoying unfailing good cheer - most of the time.
He has never allowed his pureblood prejudice to taint his work.
He allows himself to appear intolerant because the things he cannot tolerate abound in a school setting.
He doesn't tolerate whining. Weasley Junior whines constantly; about the amount of work (annoying); about his marks (his own bloody fault); about his monetary situation (for Merlin's sake shut up it isn't all about you!).
He doesn't tolerate conceit. Granger has it in spades, the interfering little know-it-all. She believes she is helping by coaching the other students, but all she is doing is allowing them to wallow in their incompetence.
He doesn't tolerate incompetence. Longbottom has come to represent that word by himself, and Severus suspects that no future student will surpass the boy in his failure. He believes that Longbottom will one day cause his own demise.
He doesn't tolerate students attempting to cause their own demise while under his care. Potter can't seem to help it, and he tends to drag his friends down with him. Snape doesn't hate the boy, not anymore, it's just that he's never lost a student under his care until Diggory, and it's not an experience he wishes to repeat.
No, Severus Snape doesn't hate Harry Potter.
He did, once. He'd never deny that. There was once far too much of James in the angular face for Severus' comfort.
But he hasn't seen James in the boy since Potter's second year, when he opened that impudent mouth and Parseltongue came out.
After that incident, his disdain for the boy became less substance and more show, less hatred and more habit. His attempts to get the boy expelled were more for the boy's safety than anything else; being at the Muggle house would offer more safety than being here at Hogwarts, and who would care if the Muggles got hurt in a foolish attack, as long as the boy or the woman lived?
Severus had thought Potter would be safest in the house where he could not be touched, and had therefore pushed as hard as he could to have the boy return to it.
Severus Snape didn't often admit that he was wrong.
He wasn't wrong this time; except for the small problem of the Muggles themselves (who apparently hated Harry for his magical gifts, bloody stupid muggles - ), Harry would indeed be safest in the house where his mother's blood resided.
As it was, Severus could now do nothing but carry on, hoping he wouldn't have to bury another boy (he's never been a boy), commit another child under his care into the ground just as he was becoming a man.
Severus Snape hates paperwork.