Plum Crazy Cupcakes

Where did the expression, "plum crazy", get its origin? I have eaten plums and they have not been particularly crazy. Anyway, Bootlegger Cupcakes made these plum cupcakes with Tallgrass Wild Plum Farmhouse Ale, filled with plum jam, finished off with an almond, honey and plum buttercream and topped with a sugar plum candy.