Reading Dune by Frank Herbert, I came across a sentence – That drunken fool of an Idaho! I know that this type of expression is usually used to render rebuke, scorn, contempt and what not. But I am not sure why the indefinite article is used here. It seems misplaced to me, because semantic of the phrase implies that there is only one man called Idaho who deserves that much of irritation, and there is no meaning of idaho-type men in it. While making my question, I came upon this answer on the site. According to it, the indefinite article is used idiomatically to suggest that a person in question has some characteristic quality applicable to all the likes. That is, all Idahoes, due to some intrinsic personal traits, are utter fools when drunk. Is it true in the case of the sentence?
Merriam-Webster lists 'fool of a' as an idiom. I'd agree ... the grammar, including the use of the article, being odd in this fixed expression. The meaning would be reasonably clear to someone meeting it for the first time. It's a snowclone, with various nouns including surnames and other class-specifying proper nouns.
There must be some denigration, if only by association, of the set mentioned, but this varies to quite an extent (brother of yours ... politician?) But I'd say that there is no great emphasis on the class the person being tongue-lashed belongs to: the class is added as an identifier ('brother of yours') and/or to add substance to the censure ("Fool!" is sufficient, but "Fool of a Took!" is memorable).
fool of a [idiom] [informal]
— used to describe a person as foolish
- Only that fool of a brother of yours would ask such a silly question!