The one thing I really love about Kimi ni Todoke is how they take all kinds of stereotypes in shoujo series and sort of turn them over.

Sawako's two best friends are the kind of characters that are typically the antagonists to main characters. A bully (Chizu) and the enjo kosai type (Yano). We've already seen that they are far more nuanced than that, but outwardly, that is how they appear. Chizu is actually pretty emotional and kind for a yanki type character, and Yano is very intelligent, and while she's nice, she certainly enjoys toying with her friends.

Similarly, Kurumi tries all sorts of nasty things to Sawako, but Sawako is just too innocent and dense to get it. She missed all of the subtext Kurumi was trying to tell her, and even twisted it around to get some good advice out of it!

'Kazehaya is nice to everyone' (You're not special)
'Just because he talks to you doesn't make you special' (she even outright says it)
'Try talking to someone who isn't as nice to everyone' (Keep away from Kazehaya)
'Everyone has their own match' (...and yours isn't Kazehaya)
'Kazehaya and I have a lot in common after all' (Clearly I am a better fit for him)

She even turns it around and stabs Kurumi with a surprised reaction that they are just friends (emphasis hers).

I really liked how Kurumi completely underestimated Sawako's naiveté. It does look like she is going to take advantage of Sawako's saintly helpful behavior. Damn you cliffhangers!