abuser, maltreater - someone who abuses

aggressor, assailant, assaulter, attacker - someone who attacks

bad person - a person who does harm to others

convict - a person who has been convicted of a criminal offence

criminal, crook, felon, malefactor, outlaw - someone who has committed (or been legally convicted of) a crime

beguiler, cheater, deceiver, trickster, slicker, cheat - someone who leads you to believe something that is not true

delinquent, juvenile delinquent - a young offender

defector, deserter - a person who abandons their duty (as on a military post)

ganef, ganof, gonif, goniff - (Yiddish) a thief or dishonest person or scoundrel (often used as a general term of abuse)

transgressor - someone who transgresses; someone who violates a law or command; "the way of transgressors is hard"

malfeasant - one guilty of malfeasance

molester - someone who subjects others to unwanted or improper sexual activities

nonattender, truant, no-show - someone who shirks duty

culprit, perpetrator - someone who perpetrates wrongdoing

fancy man, pandar, pander, panderer, pimp, ponce, procurer - someone who procures customers for whores (in England they call a pimp a ponce)

backslider, reversionist, recidivist - someone who lapses into previous undesirable patterns of behavior

miscreant, reprobate - a person without moral scruples

shark - a person who is ruthless and greedy and dishonest

pettifogger, shyster - a person (especially a lawyer or politician) who uses unscrupulous or unethical methods

evildoer, sinner - a person who sins (without repenting)

supplanter, usurper - one who wrongfully or illegally seizes and holds the place of another

war criminal - an offender who violates international law during times of war