This is a very old expression and one we often see in dated movies. I love this expression Happy Daffies because it says it all.
I have no idea of the origin of this phrase but it has been used when someone is a little over the top with a positive feeling. It has been used to describe over the top happiness to religious groups.
I think in this time of modern workings the old Happy Daffies expression is a cool reminder that life can be great.