This is a mouse with a capital M.

[Uncanny]

I wonder if and how the expression "with a capital" restricts the range of nouns and adjectives it can be used with if the speaker intends to convey a clear meaning.

For instance, would these sentences instantly produce a clear meaning in your mind:

This is a mouse with a capital M.
This is a brick with a capital B.
This is mediocrity with a capital M.
This is indifference with a capital I.
This is laziness with a capital L.
I am anxious with a capital A.
He is thin with a capital T.
They are dishonest with a capital D.
The soup is bland with a capital B.

 

[Rover_KE]

No. I'd need a specific context for each of those examples.

 

[probus]

To me the phrase "<insert word here> with a capital initial letter" signifies an extremely high level of the attribute defined by that word. It's hard to imagine a context that would call for "brick with a capital B", but the others are fine.

 

[Tarheel]

*This is a mouse with a capital M.*

Mighty Mouse?

 

[Uncanny]

To me the phrase "<insert word here> with a capital initial letter" signifies an extremely high level of the attribute defined by that word. It's hard to imagine a context that would call for "brick with a capital B", but the others are fine.

Can someone or something be 'extremely mediocre'?
John is a mediocre driver. But his wife is even more mediocre.

What you are saying is that the implied, intrinsic quality has to be quantifiable.

 

[Tarheel]

It's hard to imagine how "extremely mediocre" can work as a phrase. (See below.)

John is a bad driver, but his wife is worse.

Try that!

 

[tedmc]

I don't see the point in picking a common noun and capitalizing it. There are countless adjectives to describe nouns, like "exemplary".

 

[tedmc]

It's hard to imagine how "extremely mediocre" can work as a phrase. (See below.)

John is a bad driver, but his wife is worse.

Try that!

"Extremely mediocre" sounds like an oxymoron.

 

[Skrej]

I don't see the point in picking a common noun and capitalizing it. There are countless adjectives to describe nouns, like "exemplary".

You realize that we don't actually capitalize it, right? It's an idiom, and as such doesn't have to have a point or be logical.

https://www.collinsdictionary.com/us/dictionary/english/with-a-capital_1
https://dictionary.cambridge.org/us/dictionary/english/with-a-capital-etc

To me the phrase "<insert word here> with a capital initial letter" signifies an extremely high level of the attribute defined by that word. It's hard to imagine a context that would call for "brick with a capital B", but the others are fine.

As a masonry item, I'd agree. However, if you're referring to any number of other items bundled together (drugs, cash, etc.), then it works reasonably well. There's also a 'brick' in basketball (aka an 'air ball'), and things that are broken (especially electronic). 'Brick' is also apparently slang for a good person (possibly BrE?), and AmE regional (New England, especially NY) slang for 'very cold'. Both of those work with the expression.