GS - I consider myself thoroughly told off. It was on TV! It must be true! And you even (fail entirely) to name the program that said so!

{rollseyes}

Now try producing some real evidence. Because, of my own curiousity & volition, I went looking for a source. The only thing I could find outside of a bare defintion, is that Partridge's Slang dictionary says it is first recorded in the 16/17thC. I cannot find any explanation of the the origin of the phrase.

Not your assertion, not my supposition, not anything. So produce some genuine attributable evidence. I only suggested that "know-nothing"'s explanation was unsupported rubbish. MY theory is only an educated guess. Where's YOUR evidence?