Stacking those boxes so high is an accident waiting to happen.

‘An accident waiting to happen’ is an American figure of speech that refers to possible danger that could come as a result of the way something is done, or the way someone acts.

那些箱子疊得這麼高，就等著發生意外吧！

美語中 an accident waiting to happen 是指「有可能發生的意外」。