Honestly, this is my first time writing what I think is SasuNaru. Please forgive all silly details as I'm usually found in the NaruSasu section. Now, if that explanation didn't make any sense, all the more better for me.
Why Sasuke Hates Naruto
Two of the main reasons why Sasuke hated Naruto was because the boy was honestly far too loud and bright for his own good. The enemies would easily spot someone whose clothes just screamed "I'm right here, sucker! Come and get me!" And they usually did spot Naruto.
Those two reasons were also related to the third reason which was because Naruto really did like the attention that was given to him, even by the enemies. Little attention whore. Sasuke thought that maybe Naruto didn't know the meaning of lying low. He also couldn't understand why attention was so important. It was important for a ninja to be not known. Made their lives easier, really.
Another reason would be because, seriously, that boy was far too obsessed with ramen for it to be called healthy. Sasuke wondered whenever he went to the rest of the team – Kakashi had blackmailed him... again – to Ichiraku Ramen what exactly Naruto saw in ramen for him to like it so much to the point that he would eat it every single day for almost all of his meal times. The boy would have ramen for breakfast, lunch, and dinner if Iruka wasn't there to treat him somewhere other than Ichiraku sometimes.
One of the plainer reasons why Sasuke hated Naruto would be that Naruto was an honest-to-goodness idiot.
That reason was connected to Sasuke's Naruto-can't-recognize-people-if-they-changed-even-for-a-bit reason.
The seventh reason was because Naruto was messy. This was something unacceptable to anal-retentive Sasuke. Being messy, despite not having been in a battle, was like a sin to him. He viewed it with such contempt that it really did look like it was a sin.
One of Sasuke's favorite reasons why he hated Naruto was because the latter was just so oblivious to what other people feeling. Especially when these feelings had something to do with him. Like with that Hyuuga-girl. Of course, it had taken Sasuke a substantial amount of time to figure that one out because he sure wasn't one for love. It had helped when he heard Sakura and Ino and some other girls talking about it.
Yet another reason would be because Naruto just cared far too much about the welfare of other people. Sasuke's "avenging heart" just couldn't get why Naruto seemingly fussed over the lives of other people.
Sasuke hated Naruto because Itachi seemed to deem Naruto as more important than Sasuke... therefore that would also somewhat mean that Naruto was more powerful than Sasuke. Of course, that was only Sasuke's jealous little brother self, but still, that was one of the reasons why he hated Naruto. That was also related to one of the reasons why Sasuke lacked hatred.
Naruto made Sasuke hate him because Naruto had a scratchy-sounding voice. It irritated Sasuke. It was a childish reason but a reason nonetheless. It also made Sasuke feel something he'd much rather not talk about.
Another one of those childish reasons was because Naruto was immature and just plain silly with the pranks that he played, like the one he did on Kakashi because the jounin was late on their first meeting.
A third childish reason was because Naruto's name was just as silly as the pranks that he pulled. Really. What kind of parent would name or agree to name their son after a ramen topping? Sasuke just didn't see the logic in that one. He also didn't get why Naruto loved the name Uzumaki Naruto. Maybe it helped attract attention...?
A more mature reason was because Naruto had learned something people said was a technique that the Fourth had invented in less than a month. Sasuke – although perhaps he himself didn't notice it – was someone who was made easily jealous.
One of the inexplainable reasons why he hated Naruto was because the blond actually liked pinkie who was, of course, their teammate, Sakura. Sasuke didn't know how anyone could like someone with pink hair. It was too bright for his brooding, revenging, plotting self. Sasuke really didn't know why he hated Naruto for such a stupid reason. His other male teammate could like anyone. He shouldn't care. He really shouldn't. But he found himself caring and he didn't even know why. This reason was illogical and stupid and Sasuke didn't know why he was even accepting that he thought that this was one of the reasons why he hated his stupid, blond teammate.
The fifteenth reason was because Naruto was an uncultured little brute who didn't know manners even if it slapped him. It was the elitist inside of him screaming that reason. He, after all, was from the Uchiha Clan. That reason ought to be a given already.
The sixteenth reason was because Sasuke really didn't like Naruto's writing. It was scratchy and barely identifiable. He liked to call it chicken scratch. Of course, anyone with such great calligraphy skills as Sasuke would see such writing as chicken scratch. He was just being his prissy, elitist self again.
Almost everything that Naruto did was against the rules of being a good ninja. Shinobi like Uzumaki Naruto should be banned from getting ninja missions for the sake of his teammates who could blow a gasket just by listening to that idiot blabber on and on even though they should be quiet and all... ninja-like.
The eighteenth reason was because Naruto created the silliest (and most perverted) of jutsu. Like those stupid Oiroke no Jutsu and that one with the Harem. And what was more was that they did work and it had even beaten Sandaime and a member of the Densetsu no Sannin, namely, Jiraiya. Even though the latter was a super pervert, his ninja senses still should've kicked in.
... Sasuke then began to realize that maybe that reason wasn't good enough because Jiraiya really was a pervert and that jutsu would only work on perverts which were in abundance in the ninja world.
The second to the last reason would be because Naruto was naïve and would believe almost every piece of crap people fed to him.
And Sasuke's last reason why he hated Naruto... was because he really couldn't hate the boy no matter how much he tried or wanted to.
Thank you for taking the time out of your busy life to read this. (Despite this being what I think is a cheesy romantic cliché.)
Comments, as always, would be much appreciated. And really, don't hesitate to point out any mistakes. I'm looking for them.
I could say that this little SasuNaru bit is partially accredited to Kaikouken.
Oh, and... er... if you also read my other stories, please accept my apologies for... er... not updating. I'm having some troubles with them. So, uh, please be more patient. Thank you for sticking around with me.