Mad as a Box of Frogs

A modern, distinctly British idiom, and one whose origin genuinely isn't known despite it being fairly recent as idioms go. The image is intuitive on its face, a box of frogs would presumably produce a chaotic scene of jumping and bouncing in every direction, but no one has traced a documented first use, a coining author, or an original context. A related, possibly earlier expression describes someone as having "a face like a box of frogs," suggesting the phrase may have started as a comment on appearance before shifting to describe erratic behaviour, but that connection itself isn't firmly established either.