I'd have to say The Miz. I respect him for what he has achieved from coming into the WWE from reality TV and working his way up- he was not pushed on arrival and was with the company for a few years before getting the main event spot but as a wrestler and on-screen character he is awful.
I just have never liked him. His look and physique are painfully average, he has the face of a teenager and doesn't look like a pro wrestler in the slightest. I find the whole character annoying, irritating and even his moveset is awful. The Skull Crushing Finale is an awful finisher, and the whole "AWWWEEESSSOOMMMEE" thing is awful, not awesome.
It amazes me that WWE thought enough of Miz to give him a headline spot at WM as the Champion, and for him to actually win the match! It's no surprise though that he has fallen back down the card, as he fucking sucks.
The Miz is the reason I stopped watching WWE. At least in large part.
I don't recall who, but I remember getting in quite a number of spats with a user or two here over him "doing his job" because I'd post about how much I hated him, and how much he made me dislike WWE and want to change the channel, so much so to the point I did. Permanently. For a solid what... five, six years? I kept being told "you are supposed to hate him!" to which I'd respond, no, I'm supposed to boo him, and want to watch his matches so the faces he goes against can eventually beat him. But I don't want to watch his matches. I want to change the channel when he is on, because he is the antithesis to entertainment.
The farther he was pushed up, the further I was pushed back. He's still a guy who makes me do the same even to this day. Before watching that post-Wrestlemania RAW a couple weeks back, I remember flipping past RAW some Monday like a year ago and saying "OK, I'll give this a go". I saw Kane in the ring, and I like Kane, so I was like, sure why not. Then all I heard was "AWEEEESOOOOOO—" and I immediately changed the channel again, and never went back.
This isn't bullshit or fluff, either. I'm not even exaggerating to try and make the point stronger. I literally changed the channel, and literally stopped watching because of his face, and his character and his everything.
I nicknamed him Mizerable years ago, and that name hasn't left, even now. He's probably the only wrestler I really "hated", as to me, there's a stark difference between hatred and simply being unimpressed or not entertained. The latter hosts a slew of guys in the company the last number of years. Namely Ryback, Daniel Bryan (yes, Daniel Bryan), Kofi Kingston, DiBiase Jr., Evan Bourne, John Morrison, Otunga, pretty much anyone from NXT aside from Wade Barrett, etc. I wasn't exclusive to WWE either — Hernandez, Amazing Red, Jay Lethal, Consequences Creed, etc. all made that list too.