After reading that lipstick scene yet again, I'm going to partially disagree with myself and go along with several other folks--I just don't quite know what to make of it.
I still think the visuals suggest that probably the main dynamic is that Yamada's cuteness upgrade, slight as it is, awakens the familiar Yamada-Devouring-Monster that lives inside Kase, the one that she has so far been able to keep (mostly) in check.
But Kase's spoken lines are rather abrupt and chilling (assuming the translation gets the tone right):
"That doesn't suit you. That kinda stuff doesn't suit you, Yamada. You should stop."
Kase seems to blame Yamada for her own reaction, and doesn't even consider Yamada's own opinion about how she looks or make any move to sooth Yamada's embarrassment.
These two have had misunderstandings before, but I've never thought they weren't treating each other right. This time I felt a little more like: "That was bad."