Extremely adorable. Kind of like his own ninken. Though Kakashi isn't going to say that, because no teenager wants to be told that kitty ears sprouted atop his head are adorable. Even if that's exactly what they are. (Kakashi prefers the floppy kind of ears though. They're softer and nicer to pet. Pakkun's ears are especially cute. But Kakashi's always been more of a dog person.)
And Kakashi doesn't really consider Sasuke an equal -- he isn't, because Sasuke is a genin, and Kakashi is an ANBU captain -- but he does think that it wouldn't be very advantageous right now for him to be pissing off the only person he can trust at all. Especially when he doesn't know anything about this place other than what others have told him. And those others don't know him, and he doesn't know them. Technically he doesn't know Sasuke, either. But somewhere in the future he will. And that's enough for him.
So Kakashi picks up his ANBU mask and ties it on backwards, so that the ears point up from behind his head. Kind of like if he had ears too, sticking up from his hair. Except less furry. And definitely not moving. ]