My parents always used the expression "talking through the back of his hat". I have no idea where the expression comes from, but had always understood it to mean that the speaker had no idea what he was talking about. The implication is that it is not a deliberate attempt to mis-lead the audience, but more simply someone who appears to believe what they are saying, but in truth does not. I came across this article after a colleague Googled the expression when I used it in the office. I had checked my facts with another colleague before responding to a technical e-mail from a supplier, and said that I just wanted to make sure that when I replied I wouldn't be talking through the back of my hat. To me, this was a perfectly normal expression, but it raised a few eyebrows, and hence caused me to read this site. So, I felt it only right to put my experience forward. I shall probably visit this site more in the future, as the overall subject of where expressions like this come from is fascinating, in my opinion.