A good rule of thumb - the Wall Street Journal test. Are you prepared to have whatever you say over the phone or email (or however electronically transmitted) published on the front page of the Wall Street Journal. If not - don’t say or send it.
While I learned and practiced this in business, I’ve also tried to teach my kids this. There are a lot of people who are stupid enough to post things publicly and have paid the price - but even private communications are at risk.
Speaking as one who actually has been quoted by The Wall Street Journal, that’s a good rule of thumb!