pole
This is not a saying - it's a simile. Something is as stiff as a board, which is a stiff piece of wood. It's just a description. The term "stiff as a board" is used in many country's (in particular UK) to describe a person suffering aches and pains. Normally associated with muscular pain especially after periods of heavy work such as lifting and carrying.
Simile
A simile.
A metaphor
It is a simile.
As quick as a wink is a simile. ----
simile
simile its a simile when you use "like"
simile It is an example of a simile (uses like or as). A simile in itself though is a type of metaphor.
simile
that man