There are various synonyms for the phrase "blow hot and cold," which essentially means to alternate between two extreme behaviors or attitudes. A common phrase that can be used as a synonym is "keep changing your mind or opinion." Other synonyms include "vacillate," "flip-flop," "waver," "equivocate," "be indecisive," "dither," and "oscillate." These words convey similar definitions of uncertain or inconsistent behavior, where one cannot seem to make up their mind or stick to a particular stance. It's important to note that using synonyms can add variety and depth to your writing, making it more engaging and interesting to read.