More like, I dislike Chihiro and think she is boring because she is apathetic about life and doesn't invest herself in or toward anything. I find that attitude/outlook particularly unlikable.
Keima called her out on giving up too easily and daring to call her shallow attraction toward one guy as easily as the next, "love."
edit:
To clarify, Ayumi cares about track, Kusunoki cares about being strong or protecting the weak, Kanon cared about being noticed and bringing people happiness, Shiori cares deeply about books, Haqua cared about living up to expectations, Mio cared about her father's memory. Chihiro cares deeply about nothing. That is what makes her a weak heroine.