turn a hair, not

not turn a hair

To show no outward emotion when something bad happens or is announced. I thought he'd be devastated after losing the race, but he didn't turn a hair. You have to give Jane credit. She didn't turn a hair when the customer started shouting in her face.
See also: hair, not, turn
Farlex Dictionary of Idioms.

turn a hair, not

Not become afraid or upset, remain calm, as in She didn't turn a hair during the bank robbery. This term, also put as without turning a hair, comes from horse racing. After a race, a horse often has roughened, outward-turned hair. Its figurative use, nearly always in the negative, dates from the late 1800s.
See also: not, turn
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • not turn a hair
  • turn (something) inside out
  • turn inside out
  • turn some place inside out
  • turn something inside out
  • turn something inside out/upside down
  • stand out
  • choked with emotion
  • jab out
  • jab (something) out at (someone or something)