Nogoodnik is a slang term used to describe someone who is untrustworthy or behaves badly. If you are looking for a synonym that can convey the same meaning, you can consider words like scoundrel, rascal, rogue, troublemaker, villain, miscreant, delinquent, or even hoodlum. Each of these words denotes a person who is up to no good. Whether it's a person who is dishonest, a cheat, or a troublemaker, these synonyms can be used interchangeably with nogoodnik to describe someone who is a bad influence or is causing problems. So, the next time you want to describe someone in a more colorful way, you can use any of these synonyms to spice up your language.