Mad as a hatter

 To tell the truth
It was the top hats that did it
The milliners never needed to worry
It wasn't part of their life
But top hats had to be black
That was the fashion
So the black fingered
Hat makers
Wallowed in the mercury
Compound that made those
Black top hats so black
Breathed it in
Absorbed it through their skin
Drank it with their tea and coffee
Mercury can do terrible things to the mind
Then people started to notice
They would say things like
"He's as mad as a hatter"
And so the hatters were the unsung
Oft scorned heroes of the sartorial community