Sasuke's Nii-San
It takes Sasuke a while to realise that Itachi isn't exactly what you'd call 'normal'. He considers this for a while, and decides that if anyone ever says anything bad about his brother, he'll just punch them in the face. Not that anyone would of course, because his Nii-san is amazing, weird quirks and all.
Sasuke's brother talks weird sometimes — he always sounds so grown up and posh, and even though Sasuke knows that Itachi is really grown-up, he doesn't think he's that grown up. Or at least that's what Ka-san says to Itachi whenever he says something really funny, and then she tussles his hair, and he gets all annoyed and flustered.
Itachi can also be scary at times, like when he makes those weird scones. Sasuke's never tried one, because Ka-san says he shouldn't. Sasuke feels bad about that, but he's seen the aftermath — throwing up, hospital trips (poor Shisui), and decides that what Nii-san doesn't know can't hurt him.
If Sasuke has to pick, he'd say the weirdest thing about his brother was Flying Mint Bunny. Itachi says Flying Mint Bunny is there, even though no one else can see him, but Sasuke can't get over the weirdness of seeing his brother talking to empty air. He spends a long time trying to come up with ways of seeing Flying Mint Bunny for himself, until Ka-san pulls him aside, and tells him that maybe Flying Mint Bunny was something just for Itachi, and Sasuke should spend his time doing something for him — like training — instead of spending hours patting the empty air, hoping to stumble across an invisible green bunny.
"But how can he be invisible and green?" Sasuke asks, confused. Ka-san sighs and pats him on the head, and Tou-san mutters something about needing a drink (he's standing right next to the sink though, so Sasuke doesn't know why he can't just pour himself a glass of water).
Sasuke never does find Flying Mint Bunny.
So yes, his nii-san can be strange at times, but mostly, he is the most amazing person ever. Sure, his scones are kind of scary, but it just means that his brother is badass at everything, even at something as boring as cooking. And Itachi is super smart, and really strong, and he always takes the time to train Sasuke, even though it annoys Tou-san.
And sure, Itachi had forced him to hang around with the Dobe and the creepy fangirl, but it actually isn't too bad. The Dobe is still a dobe, but you eventually get used to how annoying he is, and Sakura isn't terrible now that they actually spent a lot of time together. They still have a lot of work but…well. They aren't that bad. So Sasuke doesn't think he can be too mad at his brother for making him hang out with them.
All in all, Sasuke thinks his brother is one of the weirdest people he's ever met, but he also thinks he is the most amazing. And that would never change, ever.