eager beaver = an enthusiastic person, a very diligent person
She is an eager beaver who wants to learn everything.
happy camper = a happy person (sometimes used to say someone is not happy)
You don’t look like a happy camper.
smart cookie = a smart person capable of dealing with problems efficiently
Ayesha, by contrast, was a smart cookie and knew exactly how to get around.
stuffed shirt = a person who behaves in a formal old fashioned way
And the marketing guy was a stuffed shirt who would appreciate formality.
a rough diamond = a person who is not well-mannered, but has a good personality
Secretly, I admired Kathy who seemed much older than me and a bit of a rough diamond.
