John Constantine was a terrible mentor. He was an extraordinary sorcerer, there was no doubt about that, but as a mentor he was terrible, and he went out of his way to remind you of that, as if he did it on purpose.

"You see? I almost got you killed... again, why are you still here, child?" John snorts, flicking his cigarette at the damaged floor of the place you and John had gone to exorcize. Sure enough, the place ended up destroyed.