Really? I love the Post man, in all incarnations.
For me, it'd have to be a close one between Kaepora Gaepora and Rauruu(yes, both of them, in that order)because they were useless and had no back story at all. I mean, hey, an owl comes out of the sky, talks your tiny Kokiri ear off, and then when you wake up seven years later, poof! He was a Sage all along. Quaint. They're just utterly useless, and they had no reason to be there except tom make curiosity kill the hero by keeping me away from the Great Fairy and telling me that I had been asleep for a while. Sheik could have told me that. I'm cool with six sages.
You know who else I hated? Linebeck III. The original Linebeck was amazing, at the end, but his grandson sucked. No identity, wasted rupees, and was only existent to do something that was pretty much unnecessary and irrelevant. I mean, hello, it's the spirit Train. THE Spirit Train. **** your Golden train.
Other than that(and Ruto, see above), I kinda got attached to everybody but Ciela. I didn't hate her, she was just not dynamic enough for a character who undergoes such a huge discovery.