Post deaf, Razor sharp... (a speacial usage of noun and adjective?)

[Duc]

Hello,
Please have a look at these sentences :
1.It's razor sharp.
2.He's post deaf.
3.It's nail tough.
I happen to read all these sentence in my book.I suppose it is a special usage of '' noun adjective'' but I don't know in which context we should use them and how to use them?
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Don't see your shade think you are great

[Yankee]

Hi Duc

The only one of your sentences that sounds natural to me is the first one.

The other two would be more natural to me this way:

2. He's (as) deaf as a post.
3. He's (as) tough as nails. (I would use 'tough as nails' to describe a person.)
.