Mad As a Hatter

Etymology:

• This idiom originated back in the early 19th century. The origin was might taken from a snake called an adder. British people assumed that if adder will bite them they will get insane. Mostly people pronounced ‘adder’ as ‘atter’ that later turned into ‘hatter’. So if you act crazy, it means you’re getting ‘mad as an atter’ or ‘mad as a hatter’. Another origin might have been taken from the felt-hat factories where people worked in the 19th century who inhaled fumes of mercuric nitrate. It caused the development of jerks, muddled their speech and grew mystified. Their condition was often taken as madness and therefore they were called ‘mad as a hatter’.