No, you misunderstand. His voice is not annoying, its Lelouch that can get annoying with his self love and arrogance at times. Don't get me wrong, I like him, but that doesn't mean I have to like everything he does.

Kei does have a lot of pride. That is not arrogant. The word arrogant itself implies that it is unjustified, and has a negative connotation. What he did with the three cheaters was completely justified and is in the bound of his skill. He did not brag about it but merely stated facts. Jun Fukuyama has a malicious tone to his voice, which enables him to play characters like Lelouch, but I thought that was unnecessary for Kei. I'd prefer him played by a less arrogant sounding voice.