I only started playing since New Leaf and I really don't like Pave. He just seems arrogant and his minigame wasn't very fun to do, especially because dancing "wrong" would have you chewed out by him.
I can't stand Shrunk. His design reminds me of that really old McDonald's character that I seem to remember from years ago, and his jokes are just unappealing. His face is so... Annoying. Everything about him is really cheesy and gives me this horrible feeling. It's weird, and difficult to explain.
I was going to say Lyle, but then I remembered Gracie. I absolutely hate Gracie. She is so rude and annoying. Her minigame in the GCN game is total BS since it requires you mashing the A button to the point where your thumb starts to spark (which in turn can cause blisters). In Wild World, she even calls the player a redneck! WTF?!
Now to talk about a hated character that I actually like: Tom Nook. Yes, I like him. You don't have to pay off all of your debt right away; you can even wait a year and he wouldn't mind. He also gave you a FREE HOUSE! How can you not accept that?! If it wasn't for the free home, you wouldn't have anywhere to live! He runs the town store in the older games too so if it wasn't for him you wouldn't be able to shop for furniture and such. Almost all (or probably all) of the theories surrounding him being a con-artist/kidnapper/slavedriver are terrible in my opinion. This character deserves a ton more praise.