M - your research is greatly appreciated! As a matter of fact, the anecdote alerted me to another name which was so obvious, I can't believe I missed it:

Willy.

It should have been right up there with "John Thomas." Again, I would think it's more a UK expression. I remember many years ago seeing Billy Connolly on television and he made some jokes about "Free Willy." Very funny - if only I could remember just what it was that he said!

Jay