「不雨則已，一雨傾盆」，形容壞事不來則已，一來則不止。It never rains but it pours 和中國成語裏的「禍不單行」意思一樣。
We had nothing to do for weeks, then suddenly we have all this work to do; it never rains but it pours!
I missed my train this morning, lost my wallet and spilt coffee all over myself; it never rains but it pours.
如果你給某人的計劃或建議「潑冷水」 pour cold water, 那就表示你的態度是太過苛刻或消極。
I wanted to walk up the mountain but Jane threw cold water on the idea by taking the cable car.