Discretion....
If I talk to you about something, and it involves another person, kindly don't turn around and relay that conversation to the other person unless I asked you to. That could be classified as a betrayal of confidence, and it's not something I appreciate. Perhaps I, too, vented, only not PUBLICLY, and don't appreciate that venting now being used against me. Maybe I didn't WANT to vent to the actual source of the frustration, maybe I recognized that there were extenuating circumstances to my own annoyance, and even expressed them in the conversation. Perhaps I didn't say anything directly to my annoyance because I didn't want what has happened: another can of worms opened. If I can't trust that my words are safe with you, I just won't tell you anything. And maybe that's what you're hoping for, I don't know.