Yukiteru Amano. 90% of what I don't like in that show comes from him, and he's easily my least favorite character in anime. He's the type of whiny protagonist that makes me wonder why people give Shinji so much shit, and the problem is that there's no real development. He has his "man up" moment at one point but it lasts for...what, an episode? And this is already near the end of the series.
Not to mention that he keeps making wrong choices and he never really learns from them, not even at the end. Instead he ends up wallowing in self pity over what I believe (or who I believe, rather) was his greatest mistake of all. Really, just thinking about it burns me up.
Probably next to him is Kirito in terms of protagonists I hate (and considering how much it takes for me to truly hate a character rather than simply disliking them or not liking them, it has weight) and Asuna more than him, and this may seem pretty bland of me, all things considered, but there are reasons. She's just an accessory for Kirito.
She (Asuna) really only has one personality, and that personality is Kirito's wristband. She had potential as a character in her early appearance, where she was just another confused character in the world of SAO- and then, I didn't mind her. She wasn't typecast to some cliche archetype or anything, she was a canvas ripe for potential. After returning to the show, she immediately became a wristband, and that potential was lost. What really made this bad, though, was the fact that she was- twice- the cause for inexplicable glitches that take you out of the experience, and that her relationship with Kirito was...perfect like a love song. Perfect, in that there was no real foundation for the relationship, and it felt very one-dimensional in that there was nothing else to it- it was just love for the sake of love, just like a love song would depict. All they needed was each other, and they never had fights, talked about anything in particular other than SAO or Yui, and, again, it didn't really grow from anything other than that Kirito was a guy and Asuna was a girl. It had no chemistry, and like the two involved, it didn't have any sort of personality. And normally I wouldn't be too hung up on this, but this- as in from episode 6 onward- is where my feelings about the show started to change.
When you give a character a wristband, naturally they change too. They have an obligation to acknowledge said wristband- either sexually, romantically, or both- and at times they become one with the wristband. Thus Kirito was made a husband, but the kicker is that now that the camera was shown more on him as a character, it was more dependent on...him as a characte-
Wait a minute, this is unnecessary. Yuki, Kirito, and Asuna, those are the three, and though I finished SAO 1 and technically finished Future Diary, I also technically dropped Future Diary and am unsure about whether SAO 2 is going to happen for me. Though I rarely feel the need to objectively trash characters, mainly because it seems excessive and insulting, I really think these three are just really badly written characters that only get worse as their series' progress. As for someone I do like that's hated...Rossiu from TTGL. He's kind of like a better written Yukiteru in that he's kind of whiny, but the main reason he's like this is because he's the straight man in a group of people that like to kick logic to the curb. Later on he also makes bad decisions- ones that are fatal even- but the reason I like Rossiu is because he comes to terms with this and tries to change as a person, and similarly he also tries to redeem himself rather than simply wallowing in self-pity.
Getting slapped in the face helped.