Some characters I disliked reading about have been already mentioned, such as the Patriotists. Then there was the Senior Assessor.. He's so pointless o.O Or Syrrin Kanar. Not because him murdering Trull [though I loved Trull], but because his few parts were really annoying. Rautos Hivanar and Atri-Preda Bivatt can be count to the annoying-to-read-about ones, too. And for some reason - I can't explain why - I disliked reading about Rud Elalle. Although not a bad character I wished I could somehow skip him.
Furthermore there are Felisin [self-importent bitches, both Felisins], Baudin, Lady Envy [oh, I liked Toc, but not this damned Lady], Smiles, and some others I can't recall now 'cause they weren't really important. Of course, there are characters I disliked and/or hated because of how they acted and what they said, but that doesn't actually mean reading about them was boring [e.g. Kallor, he's a big evil nasty guy, but he's some kind of fun]. Not much fun were the characters - especially in RG - that were introduced only to be butchered on the next page.
Well, one character I really hate now and hope she'll never show up again [although it's not very likely] is Apsalar. I kinda enjoyed reading about her most of the series [at least I had no negative feelings regarding her], but as she showed up at the end of BH and transformed about a hundred or so Claws into bloody mist before killing Pearl... well, that was the top of the iceberg and I nearly threw the book at the wall... Not nice, not nice at all