The quality or state of being an asshead; extreme foolishness or stupidity.
From asshead + -edness suffix (from -ed + -ness, creating abstract nouns for qualities or conditions). This chains together multiple suffixes to create a term for the characteristic of being foolish.
By adding -edness to asshead, English speakers created a noun that treats stupidity as a describable condition—like saying 'his assheadedness was on display'—which is both insulting and oddly clinical.
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