There are a few I don't really hate per se, but was disappointed in. I really love Swirlix, Spritzee, and Braixen...oh man, especially Braixen. Favorite gen VI Pokemon. But I am disappointed with all their evolutions. I mean, they're not terrible and I think they're okay, but I was expecting better with them and it makes me not want to evolve them. :( I'm pretty fond of my Slurpuff and Delphox personally, but I haven't really touched Aromatisse...I think of the three I named, that's the one that disappoints me most. I was hoping that Spritzee, looking happy and cute, yet somehow still creepy, would become a more...morbid, dark purple/fuchsia kind of thing? There was great fan art back before Aromatisse was revealed. I guess Google for it.
The Pokemon I absolutely do not like are Binacle and Avalugg. Barbaracle is a great Pokemon to use, and while I don't like the design, the Pokemon itself grew on me because it was a great team member. But Binacle is still...wow. Named mine God Forsaken. lol And I like Bergmite, but Avalugg is probably the most uncreative thing I've ever seen. I normally don't say that about Pokemon, because I usually can find something about them I really like, but this thing...I just can't find it any saving grace. It's a table of ice and looks like it wasn't even made by a human being. It really looks like they didn't even try. If anyone wants to tell me something great about Avalugg, be my guest. I like Bergmite enough to hope for something good about Avalugg.
So, all that being said, my #1 hated gen VI Pokemon is Avalugg. #1 disappointing gen VI Pokemon is Aromatisse.