First of all I wanna say that even the craziest most removed from reality enemies in Naruto have deep meanings associated with their madness, despite sometimes making them less fully relatable. Also being crazy has nothing to do with intelligence or cleverness.
1-Fairly Sane
Itachi
Kakuzu
Danzo
Zabuza
Sand Siblings (minus crazy Gaara)
2-slightly insane
Post Itachi battle Sasuke
Kisame
3-pretty crazy
Obito
Sasori
Konan (for sticking it out with Nagato)
4-lunatics
Madara
Nagato (could be argued a bit less)
Deidara
Crazy Gaara
Orochimaru
Kabuto
Karin
Toneri
5-Completely insane
Kaguya (and Black Zetsu)
Hidan
Pissed off Crazy Gaara
Kimmimaru
1-Fairly Sane
Itachi
Kakuzu
Danzo
Zabuza
Sand Siblings (minus crazy Gaara)
2-slightly insane
Post Itachi battle Sasuke
Kisame
3-pretty crazy
Obito
Sasori
Konan (for sticking it out with Nagato)
4-lunatics
Madara
Nagato (could be argued a bit less)
Deidara
Crazy Gaara
Orochimaru
Kabuto
Karin
Toneri
5-Completely insane
Kaguya (and Black Zetsu)
Hidan
Pissed off Crazy Gaara
Kimmimaru
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