It's allegedly an old Scottish song that the English stole, stuffed up the words, and now claim that it doesn't make any sense! The English thus claim that the song is about stupid fools.

The alleged original had as a chorus "Who's fu' the noo?" - literally "Who's full now?" meaning "Who's drunk now?" The English botched it to "Who's the fool now?".

When you look at this, the things traditionally sung as being seen are those a drunk traditionally sees, not a fool.

Of course, a drunk may be a fool too, I suppose...

Robin