I had a situation similar to this while redoing the Mages Guild recommendations today! It was the Anvil quest where I'm supposed to stop whoever has been killing the merchants. So I run up to the battlemage inside the inn, who was standing right next to the Altmer that's murdering everyone. We talk about my undercover mission right in front of the criminal. Either that Altmer woman is an idiot, or she just really didn't care that it was a trap.

what about " when you get the chance, kill that false idiot, he deserve it! AND your pocked its going to be a little bit heavier!" yea definitly the other guy would try to change subjects...(just an example and insert guy's name somewhere in the dialog)

Yeh but you could also say that Npc1 said that Npc2:s mother is a horse to Npc2

Epic. That's really something that needs to be thrown out of the door asap. But it would take lots and lots of time to make the NPCs react and recognize that you talked abou them, so instead Bethesda could simply lower the voice of the NPC you are talking about if the person you are talking about is in the same room. Or maybe not use his/her name.