fraidy-cat → leopard spots
a fraidy-cat (a fearful person): Don’t be such a fraidy-cat, dive into the water.
a grin like a Cheshire cat (a very wide smile): She walked in here with a grin like a Cheshire cat.
a harebrained idea (a foolish or stupid ideal): In such a cold weather; jumping into the water was a harebrained idea.
a horse of a different color: I love astronomy, but geography is a horse of a different color.
a kangaroo court (an unfair and illegal court): He was to face a kangaroo court in the jungle.