blow是吹的意思，hot是热，cold是冷。blow hot and cold表达的意思却是不断改变主意、摇摆不定、喜怒无常、出尔反尔。

【例句】
In our many dealings with the police, we have found that they can blow hot and cold.
在我们多次和警察打交道的过程中，我们发现他们可能出尔反尔。

Mary blow hot and cold about her job; every day she changed her mind.
玛丽对于工作的事情拿不定主意，她今天想这样，明天又想那样。