When is it socially acceptable/unacceptable for person A to say anything to person B about person C, when person C is already in the room, if ever?

Also, what about when person A answers questions directed at person C, before they can even respond?

Never acceptable imo.

It's acceptable all the time to talk about anybody, regardless of where they are.

If you done it when Person C was absent they'd then call you two faced or a backstabber, so stuff them, talk [censored] about them while they're there and in earshot. Make their little ears burn up.

I don't think its a matter of "socially acceptable or unacceptable", it depends on person A's character. Does person A prefer to gossip and discreetly express opinions, or does he/she prefer to say it outright. Its pretty strange for person A to do what you said though, sounds like person A has some ulterior motive

But anyway, my baseline is that it isnt unacceptable to comment on others negatively. So it doesnt really matter how you do it (as long as no purposeful and malicious hurting is involved )

Think about it this way, at least you know what they are saying about you and your not getting it second hand.

This. It depends on who's talking about who, and what they are saying about the one they are talking about. If it's negative comments, it's true that they might hurt you of piss you off, but at least you heard them from their original source and not from a third party.

Right.

Person A is looking for attention, I guess. I only tolerate it because I don't like to chide people.

Depends on how butthurt Person C tends to get over things like that.

Not to seem like I'm making fun of anyone with that remark, I just think people can be a little too sensitive over small things like that sometimes. But it's better to save yourself the trouble and only do that if you know which friends wouldn't mind it.

I prefer if someone has something to say to me, say it to my face, you'll either get a knuckle sandwich or an understanding. I hate people who talk bad about me behind my back and I'm in the same room .

I talk behind people's backs all the time, but at least I have the guts to say it straight to person C's face if *he notices. When is it socially acceptable/unacceptable? That depends entirely on what person A tells person B, in which general ethics apply, and since we don't know I'll just say no, it's not wrong in itself.

It's always struck me as pretty rude and aggressive behaviour, but ymmv I suppose.