"Be lucky for you if I didn't." Luke responds, feeling particularly childish. Yeah, so what if he's basically saying 'no you' what else is he supposed to say or do right now?

You took his paper he couldn't write notes even if he wanted to! Which he most certainly does not, because now that'd be like following his orders and that's not gonna happen.

So instead, Luke just... scrunches down into his seat, arms crossed over his chest and eyes defiant. You're not the boss of him. You can't tell him what to do. So there!

Basically acting exactly like the teenager he still is.