blow hot and cold字面意思是“吹热和冷”，那就是忽冷忽热的意思，可以意为拿不定主意，反复无常，摇摆不定，犹豫不决。

【例句】
Some people can make up their minds right away, but others blow hot and cold.
一些人能很快下决心，可另一些人就老是犹豫不决。

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。