mad as a hatter

"as mad as a hatter"

definition: completely mad

(šílený)

example: "That man talking to himself over there is as mad as a hatter!"

origin: Mercury used to be used in the making of hats. This was known to have affected the nervous systems of hatters, causing them to tremble and appear insane. The use of mercury compounds in 19th century hat making and the resulting effects are well-established - mercury poisoning is still known today as 'Mad Hatter's disease'.