Stiff as a poker - Idioms by The Free Dictionary
stiff as a poker
*stiff as a poker
rigid and inflexible; stiff and awkward. (Usually used to describe people. *Also: as ~.) This guy's dead. He's cold and as stiff as a poker. John is not a very good dancer; he's stiff as a poker.
(as) stiff as a ˈpoker (informal) (usually of people) very straight or upright in the way you sit or stand: The old lady was sitting upright in her chair, stiff as a poker.
References in classic literature
Come here, Amy, and do the fainting scene, for you are as stiff as a poker