I started off thinking that this character was actually not annoying at all. On the contrary: I pitied him and hoped that everything would turn out alright for him. But soon this sympathy changed into feeling annoyed because of his ignorance and his personality. I’m talking about Ganta from Deadman Wonderland.
I can’t remember when exactly I started to hate him, but it was probably somewhere around the middle of the anime. One thing that annoyed me already from the beginning was his voice. Don’t get me wrong: I’m a fan of Romi Paku, and I think she did a great job voicing for example Captain Hitsugaya in Bleach, but somehow the voice and the character did not match this time. I was also immensely annoyed by Ganta’s lack of judgment and his insecurity all the time. I get it, he’s a young boy in a prison full of life-threatening devices and games, but still it does not make up for his behaviour throughout the whole anime series.