Nutty as a Fruitcake

Etymology:

• The origin of this idiom dates back to America in late 1920s. In the expression the adjective “nutty” was used a slang for a foolish person. A slang “nut” is also used commonly for someone who extremely eccentric in his behavior. The similarity to fruitcakes is clear as fruitcakes contain nuts as well. So the expression “nutty as a fruitcake” refers to a person who behaves in a strange manner.