the.com/cad
a gentleman's manners wearing a scoundrel's intentions.
means a man who behaves dishonorably, especially toward women, while maintaining a veneer of charm or breeding.
from short for cadet, once meaning an unranked helper or younger brother of a gentleman; by the 1700s it meant a low fellow, and by Victorian times it had settled into its current meaning: a man of good manners and bad intentions.
original slang19th century oxford students used it for townsfolk
class insultimplied fake gentility, not just bad behavior
decline in usepeaked in edwardian novels, now mostly archaic
for instance
george wickham — pride and prejudice villain who seduces and abandons
john willoughby — sense and sensibility cad who jilts marianne dashwood
barry lyndon — thackeray's antihero, a social climbing charmer and rogue