Does it mean "Hino-san's idiot" (indicating possession) or "Hino-san is an idiot"?
If it's the latter, why shouldn't it be "Hino-san は baka"?
Does it mean "Hino-san's idiot" (indicating possession) or "Hino-san is an idiot"?
If it's the latter, why shouldn't it be "Hino-san は baka"?
The の is appositive (同格). The Wiktionary entry for の may help:
の
助詞
格助詞
5. 上の語と下の語が同格であることを表す。
- 部長の山田さん。
- 妹の薫さんが来てたよ。 (...)
- 悪態をつくときに用いられる表現。
- お兄ちゃんのバカ。
- 部長のわからず屋が。
The appositive の has been explained multiple times in this site:
Common/familiar examples:
『羊のショーン』 Shaun the Sheep
『おさるのジョージ』
『セロ弾きのゴーシュ』 Gauche the Cellist
「妹のメイです。」
「魔女のキキです。こっちは黒猫のジジ。」
The Wiktionary page says one of the usages of the appositive の is 悪態をつくときに用いられる.
This has also been asked in this site:
Common examples:
「メイのばか!もう知らない!」「お姉ちゃんのバカー!」
「ばあばのケチ。もうやめなよ。」
「クララの弱虫!」
「ペーターの意地悪。」
「おばさんの嘘つき!」
There are various opinions, but my conclusion is "this construction is hard to explain perfectly based on simpler grammar rules". I can say the following sentences are all valid:
の in Sentence 3 is clearly not a substitution of the subject marker が/は; the subject of this sentence is undoubtedly 太郎のバカ as a whole. However, の in Sentence 2 doesn't seem to be an apposition marker to me. Unlike バカ ("idiot") which is a noun that can represent a person, エッチ is a na-adjective and cannot represent a person. We can say バカが3人いる but not エッチが3人いる.
Therefore, I think it's best to regard this as a special construction that can be used only in the context of abusing someone, like English "You idiot!". "太郎の天才!" is understandable but sounds like a joke to me.
Possession is just one of the many meanings of の, and does not apply in this case.「ひのさんのバカ」 here means ひのさんがバカ, i.e. "Hino is an idiot" (as you suspected).
See: How does the の work in 「日本人の知らない日本語」?
While this substitution mostly applies to relative clauses or double-subject constructions (unless there is a direct object marked with を), the subject particle が can be replaced with の in many cases.
Refer also to the Jisho definition for の
1. indicates possessive (...)
2. nominalizes verbs and adjectives (...)
3. substitutes for "ga" in subordinate phrases. (See also が): 100人近くの人がいたが、ほとんど会ったことのない人たちだった。There were almost 100 people, few of whom I had seen before. (...)