Doing such a thing is the height of rudeness.
His attitude is the pinnacle of negligence.
one's true worth; one's true self; what one is really made of
Standard kanji spelling.
Rarely used kanji form.
The kanji 骨 (bone) and 頂 (top) combine to suggest the 'topmost bone' or 'core', figuratively meaning the extreme or pinnacle of something. The reading こっちょう is a regular on'yomi compound.