mad hatter is a colloquial phrase used in conversation to refer to a crazy person. In 18th and 19th century England, was used in the production of , which was used in the manufacturing of hats common of the time. People who patronised these hat factories were exposed daily to trace amounts of the metal, which accumulated within their bodies over time, causing some workers to develop dementia caused by (called ). Thus, the phrase became popular as a way to refer to someone who was perceived as insane.
