Itachi has seen him around; a couple of times when his father was invited to
the Hyuuga compound; in the halls of the Ninja Academy when he assisted to a
parents' reunion instead of his father; at the Chuunin exam, he thinks, where
he lost to his little brother's too-loud teammate. He hasn't paid much attention.
Hyuugas tend to resemble each other rather a lot.
When Hyuuga Neji is assigned to his ANBU squad, Itachi isn't overly impressed. Neji has a reputation as having a chip on his shoulder and no sense of humor.
Not that Itachi has any, from what his teammates say. (The last time they saw him expressing outright amusement, he ended up undergoing an early mental health evaluation.) But most people need to laugh sometimes or they eventually break, and Itachi has no time to waste, no care to invest in protecting a teammate who's going to break before he can adapt to the demands of the job anyway.
Neji is rumored to be a genius, though; and Itachi so often grows weary of mediocrity. So he watches.
Neji is a genius -- but one who doesn't believe in sparing himself. One who constantly pushes and pushes his own limits.
And Itachi, who has been falling into a dulling routine full of quickly smothered dreams of real power, feels like he's waking up. He's been chomping at the bit, waiting for his little brother to catch up for so long -- no one else he knows has the potential and the drive, but Sasuke is a late bloomer and Itachi is starting to reconsider his old choice.
He wonders how far the Hyuuga can follow. Probably he will never reach the heights Itachi himself knows he is capable of; the Hyuugas' power is mostly based in Taijutsu, which is fairly limiting, in the end. But in the meantime, he might prove to be an adequate temporary foil.
Neji surprises him. Neji's Taijutsu starts off inferior to Itachi's, for the simple reason that Neji still fights, sometimes, like he's sparring; and even when he's sparring Itachi always fights like he's fighting to kill.
Neji gets over that damn fast.
Besides, Kaiten is unexpectedly practical for dispersing many kinds of Katon. And the strength and precision of those strange jets of raw chakra he's experimenting with keeps growing. Itachi wonders, sometimes, whether Neji would even disperse the black flames of Amaterasu, or whether they would devour him alive.
He doesn't test, not yet. He watches as Neji grows stronger, and he prods him along, and kills everyone who tries to kill Neji. Neji isn't allowed to die until he reaches his full potential.
Unsurprisingly, they often end up partnered.
Neji's sharp intellect is appealing, his views on life and its meaning intriguing; his emotional restraint a welcome relief.
More often than not, he gives as good as he gets. So Itachi gives; perhaps more than he intended, at first. But he's still waiting for the day he'll regret it.
Besides, witty sarcasm and a fine appreciation for Schadenfreude are perfectly acceptable forms of humor.