blow hot and cold
出尔反尔
A：Look! The girl is so beautiful and she is smiling at me. She is lovely!
A: 看!那个女孩真漂亮，她对我笑呢。她真是可爱!
B: I can't agree with you. She's pretty, but she always blows hot and cold.
B：我不同意你的看法。她是很美，但她也总是喜怒无常。
A: What makes you think so?
A：你怎么会这么认为?
B: She's my sister, you know.
B: 你知道吗，她是我的妹辣。