This manga has become like an accident scene: disgusting, but can't look away.
Itagaki is by no means the only offender (and he was not even a problem when he first entered the story), but he is definitely the worst now. Being generous, one might say that his abilities are severely exaggerated expressions of reality, and they along with his cocky attitude make him an insufferable and downright boring character. However, I think it would be fair to say that some of his abilities are downright ridiculous and impossible.
And like I have said before about some of the other ridiculous, reality breaking aspects (e.g. the state of Kimura, Aoki, and Takamura's fights), it completely undercuts any message or meaning one might get from the great fights (Miyata's, some of Ippo's, Mashiba's, etc) or the character building moments.