I think you should have waited to be asked by your friend. Not even brought it up in casual conversation.
Should have let him ask you, and only answer the questions he asks you, never anything beyond that. If he asks you too general a question like, "What's he like?" Ask him to narrow it down. Only respond about specifics. Basically I'm in agreement that the golden rule is, "Speak when spoken to."
I'm certain this actor will find work in the future and that your friend appreciates your input whether or not he asked. In the future I would practice some restraint. As much as we want to see karma in action we can't make it happen ourselves, because it'll come back in bite us in the you know what too.
