not turn a hair 不动声色；镇定自若；不畏惧；难关又面不改容

【例句】
When the general received the news of the army's defeat, he did not turn a hair.
将军获悉部队战败的消息后, 依然镇定自若。

You have to give Jane credit. She didn't turn a hair when the customer started shouting in her face.
你得相信简。当顾客冲她大喊大叫时，她面不改色。