jack in
A person who’s good, but when you push them, they turn into a total monster, like Baby JackJack from The Incredibles.
My little brother is a JackJack, he’s good, but when you tease him, he turns into a monster.
My crush is a JackJack, she’s sweet, but when you say something mean, she flips.
My mom is a JackJack, she’s cool, but when you mess with her, she gets super angry.