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Anoon2323: He's saying that Kaoru, being self-aware that she's a commoner, will only cause chaos (through the resulting political storm from nobles taking sides for/against her) if she engaged the prince due to difference in their statuses, and going so far as to talk shit to him + scarred her face just to make her point.
So basically to summarize the flow of things:
K "Dafuq? You can't propose to a commoner"
P "A noble can adopt you"
K "Should've had that happen BEFORE ENGAGEMENT" (remember that the prince was about to introduce her as his official fiancee i.e. making them engaged officially as well)
*proceeds to trashtalk about system of nobility*
K "So yeah, I'm not fit to be Queen"
P "But I just want your smarts and your looks"
K "VERY WELL" *slice face* "WHAT NOW?"