Disclaimer: HP and his groupies are not mine.
When Harry hates, he does so with a passion. His blood runs hot in his veins, searing him from the inside out until he thinks he might burst into flames. His vision goes red, and his hands curl into fists so tight that his fingernails bite into his palms and break his skin.
When he hates, his mind seems disconnected from the rest of him, and all the words he wants to say crumble to ash on the back of his tongue before they can escape his lips. Instead, he snarls almost incoherently, snapping out harsh, angry comments to counter whatever insults he receives.
At times, it is almost as if he ceases to function properly and becomes something base, animalistic, driven by emotion and instinct and void of higher thought, something stitched together of shadows and fury. He wants to snap Malfoy in two, he wants to hear Snape beg for mercy, wants to obliterate Voldemort so utterly that not even a murmur of Riddle remains. He wants the satisfaction of blood staining his hands and screams ringing in his ears.
Neville tries to warn him. "People tend to become what they hate," he says solemnly, sounding eerily like Dumbledore for a moment. Harry shrugs him off, dismissing the comment as ridiculous and out of place.
When Harry hates, he doesn't listen well to others.
And when he hates, he gets revenge.
It's Lestrange, trapped in a Ministry cell, who gets the brunt of his rage. He proves conclusively that he is indeed sadistic enough to enjoy another's pain, listens calmly as she screams, then ends the Cruciatus when she finally stops moving.
He stares at her for a second, wondering if she's even alive, then manages to get halfway to the cell's locked door before he vomits.
The Aurors don't say anything when he emerges, but he's sure he sees approval in more than a few gazes. He barely manages to make it back to Grimmauld before he's sick again.
When Harry hates, it's as if the core of him, all light and brilliance, has been dimmed to shades of darkness. It's as if his true self is buried under spite and loathing and anger.
And when the anger is spent and the spite expressed, when a madwoman is left broken on the ground, Harry is left with nothing but loathing. But not loathing for the woman in the cell, or for Malfoy or Snape or Voldemort.
Now when Harry hates, his enemy is himself.