From Taiwanese Hokkien (Tai-lo: ku-moo), now common across Chinese-language internet. Originally a Buddhist phrase 龟毛兔角 'turtle hair, rabbit horns' — things that don't exist — but in modern slang it just means a fussy, hard-to-please person.
memory
Picture someone splitting hairs about a turtle — turtles don't have hair, so caring about turtle-hair details is the ultimate nitpick.
