She's got a terrible intelligence streak, and it irks him to no end. If it weren't for the fact that he and Harry stuck with her after saving her from that troll, Ron's pretty sure that Hermione a) wouldn't have friends and b) would turn into a mini-version of Pince before anyone could say "at least we didn't get expelled."
But now he's pretty sure he's got a crush on Hermione Granger, and Ron has to wonder if that's as bad as it sounds. Because she can't be a Know-It-All all the time, right?
And Ron kind of likes that.