"You fool," said Lupin softly. "Is a schoolboy grudge worth putting and innocent man back inside Azkaban?"
BANG! Thin, snakelike cords burst from the end of Snape's wand and twisted themselves around Lupin's mouth, wrists, and ankles; he overbalanced and fell to the floor, unable to move. With a roar of rage, Black started toward Snape, but Snape pointed his wand straight between Black's eyes.
"Give me a reason," he whispered. "Give me a reason to do it, and I swear I will."
That was from Prisoner of Azkaban , when Snape shows up in the Shreiking Shack.
This makes me really mad, because I wouldn't call it a "schoolboy grudge." I think Snape had a right to hate him, considering how James and Sirius tormented him as a child, and it's their fault that Lily stopped being friends with him. So if you call that a "schoolboy grudge," then yes, it's worth it. Hell, I would do the same. Besides, when have you ever known Snape to care about the fate of other people?
And the last part is really emanating with anger- So much that I feel Snape's anger. How would it feel to finally confront the people that made your life the Hell it is today, and have them completely at your mercy? You'd be filled with unfathomable rage the moment you saw them, but once you had them all in the same room, and you're the only one with a wand... You'll go insane with revenge.
