I agree with all the points made above... but I was referring to another form of subtle embarrassment that you probably don't even realize you are doing when you speak to someone in a friendly tone.

Consider this situation...you are having dinner with a couple that you are close friends with. The husband is telling you about the new porch he built, using a certain design. You know from your own experience that this design has some technical issues to it, and that it may in fact not be legal in your area...do you tell him this?

Most people would say something right off the top of their heads without evening thinking about it. What I am saying, is that, knowing that the porch is already built, there is no point in bringing this up right at the moment when the guy is excitedly telling you about it. Also, if you do so, you are immediately going to make him look bad in front of his wife = never do this. So you should just nod your head and tell him that it is great.

Later on, when you are in private with him, if you really feel he needs to know, you can mention that you have a magazine that talks about all the new types of porches out there (and which you know talks about this legal issue). The guy will find out about it on his own, in due time, as there is no real rush at this point. And you will have helped your friend, without embarrassing him. He will see you as a helpful person who he can trust and share information with, rather then someone to be guarded around.

Most people wouldn't do this though...they would just blurt something out... and they would really embarrass their friend without thinking about it. This is the sort of subtle embarrassment that I am talking about. This is what I try to avoid doing these days.