There were several reasons as to why Deidara hated Itachi Uchiha.
One, Itachi mocked his art. Sure, it wasn't openly, but Deidara swore he could hear the weasel's voice in his head, ridiculing, dismissing, taunting. Calling the blond
asinine and immature, even. It drove him wild. The Uchiha was an arrogant bastard, who clearly thought little of anyone other than himself, no matter their strengths over
him.
Which brought Deidara to the second point. Itachi was cold in both his presense and demeanor. Somehow, this "cold" air gained the raven more attention, more
admiration. The genius, Itachi Uchiha. Konoha's prodigy, Itachi Uchiha. Deidara felt overshadowed, belittled.
Third, he was just so damn brilliant. Even Deidara had to acknowledge it, seeing as the sharingan-wielder had beaten him in only a few moves (a fourth reason for the
blond to hate the Uchiha.) Book-smart and street-smart. Brilliant, actually. Deidara was jealous. Itachi sickened him, in a way, because...
...five. Itachi Uchiha was just so goddamn perfect. And Deidara despised him for it.
Yet for some reason, the blonde couldn't help but hold a twinge of admiration for Itachi. Albeit it was hidden behind extreme rage and outstanding envy, it was there.
The feeling of awe. And Deidara knew he felt something for the raven, he did, but he could never distinctly make out what. It was aggrivating, knowing that you hold
something for the one being you hate more than anything, and not knowing what exactly it is. It seemed as much as Deidara tried to muse his feelings toward Uchiha,
the only things that would ever come out of it were hatred and that unknown feeling.
Deidara couldn't pull his mind off the subject. He hated Itachi.
But there was part of the bomber that couldn't help but love him as well.
Alright, what d'you fucking think? R&R please, bitches. :) I had this idea at fucking 3:00 am, and I just couldn't fucking get it out om my head.
~Hollow-Kuchiki

1