"Look, little brat of mine," John starts the conversation with a stern fatherly look on his face which doesn't match him at all, "I get this rock/metal phase of yours, I had it myself, but you are being extremely reckless of your magic." He says, not delighted with your stupidity. You have a much stronger magic than him and Zatana together, and you aren't taking it seriously, at all. As a father, he has to stop you before your recklessness could hurt anyone, even yourself.