Wiktionary
brattiness
n. The state or condition of being bratty.
Usage examples of "brattiness".
I wish I could make him forget to be a brat, but without his brattiness he would disappear, because that's his essence.
Godorov was prepared for that—in the face of the boy’s brattiness, witnessed by everyone on the train, his accusation would be seen as just another silly tantrum.
Selenay told me that her marriage with Elspeth's father wasn't a good one, and that she felt that a lot of Elspeth's brattiness is due to her own neglect.