late 13c., "coarse, rough" (of surfaces), from Old French ruide (13c.) or directly from Latin rudis "rough, crude, unlearned," a word of uncertain etymology, related to rudus "rubble." The usual preferred derivation is that it is from the same source as Latin rufus "red" (see rufous) via a notion of raw ("red") meat, but de Vaan points out "there is not a shimmer of a meaning 'red' in rudis or in rudus 'rubble', so that the supposed shift from 'crude (meat)' > 'crude' rests in the air."
Sense of "ill-mannered, uncultured; uneducated, uncultured" is from mid-14c. Rude boy (also rudie, for short) in Jamaican slang is attested from 1967. Figurative phrase rude awakening is attested from 1895.