A person of thoroughly bad character.
Finally, on the verge of physical and financial ruin, the reprobate dropped his lowlife friends, joined AA, and begged his wife to come back.
Reprobate (which includes the prefix re-, "back or backward") is often said in a tone of joshing affection. The related verb is reprove or "scold," since the reprobate deserves a constant scolding. Shakespeare's great character Falstaff -- a lazy, lying, boastful, sponging drunkard -- is the model of an old reprobate.