Like a cat on a hot tin roof.
As you might guess, this means to be nervous and agitated.
The phrase was made famous by playwright Tennessee Williams with his play of the same name. His work generally showed tense, repressed relationships where the people were like cats on a hot tin roof!
How can you use it?
To describe somebody who is very anxious - often when waiting or anticipating something.
The expectant father was like a cat on a hot tin roof waiting for the birth of his daughter.