骨こっ頂ちょう

noun

height; pinnacle; acme

Used in the pattern 〜も骨頂だ to mean 'the height of ...' or 'the ultimate in ...', often with a negative or critical nuance.

• そんなことをするなんて、無ぶ礼れいも骨こっ頂ちょうだ。

  Doing such a thing is the height of rudeness.

• 彼かれの態たい度どは怠たい慢まんも骨こっ頂ちょうだ。

  His attitude is the pinnacle of negligence.