You start yelling

"You little bitch!" you squeal, jumping up in pretended fury. "You'll keep your mouth shut!"

"I'm gonna tell Mom that you had Mr. Thornhaven's thing in your mouth!" Jenna answers, sticking her tongue out at you, fully into her role as the bratty little sister.

"Don't you dare! I'll kill you! You get out of here and keep quiet!"

"Make me!" she sneered, sticking her tongue out again.

"Bring the little brat over here. I've got something to keep her quiet!" Mr. Thornhaven growls.