Every character in Final Fantasy X-2 annoyed me aside from a very, very select few, but Yuna outranks them all.

Aside from her, I really disliked Tifa. Vincent comes in a distant third, only because of Dante Syndrome. (I know, technically he came first, but it doesn't mean he can't have the syndrome or star in his own game because he has long black hair, a cape, and a "badass" attitude.)