Starting in the 17th century hatters lost their minds. It turns out they were being poisoned. Back then hats were almost always made from felt. Hatters made their own felt using a process called “carroting”. This involved separating fur from animal skin. Hatters used mercuric nitrate to help the process along. This exposed them to mercury vapors. At the time people had no idea how harmful those were. Once inhaled the lungs absorbed the mercury vapors. It then entered the blood and ultimately the brain. The effects include:irritability, low self-confidence, depression, apathy, shyness and timidity and in some extreme cases with prolonged exposure to mercury vapors, delirium, personality changes and memory loss occur as a result, sometimes even death.
So if you know an Irritable hatter, they have no Excuse !!!