Her Obsession
He could never hate any part of Rin. She was his life mate, and he loved her. So he wouldn't say that he hated it that whenever they saw his half brother she had to tweak his ears. He just disliked it. Sesshoumaru was sure that his brother hated it.
So she had an obsession with dog ears, so what? It wouldn't bother him so if it was anyone but him.
She liked it so he didn't say anything. But sometimes Sesshoumaru wonders, if maybe she knows. Maybe Rin just does it to get under his skin? But what purpose could it possibly serve? Nothing comes to mind. Well, after every time he reluctantly visits his brother he claims Rin again. Rather roughly too. It was probably all in his head though. She would never-no Rin was far to innocent for that.