You casually ask him if he knows anything about the diamond you seek, and he instantly becomes very unfriendly.
'Oh, no, I don't talk about that, I'm afraid,' he says coldly, glaring at you. 'Respectable people leave that well alone. I suggest you leave now, if you don't mind - I'm extremely busy.'
You try to apologize and ask him about something else, but he won't talk to you any more. He suddenly seems very menacing, even though he's just an old man, and you decide you'd better leave.
You go back outside to the corridor.