means behavior that is impolite, disrespectful, or offensive to others, ignoring the social courtesies expected in a given situation

from From 'rude,' which entered English in the 1300s through Old French 'rude,' from Latin 'rudis' — meaning rough, raw, unworked, unpolished, the way a block of stone is before anyone takes a chisel to it. The same root sits behind 'rudimentary.' So at its core, rudeness is simply the unrefined state: the human equivalent of a thing left coarse and unfinished. The suffix '-ness' came along later to name the quality itself.