bad apple vs black sheep

bad apple

noun
  • A person who is not wholesome, honest, or trustworthy, especially one who has an adverse influence on others. 

black sheep

noun
  • A person who is not wholesome, honest, or trustworthy. 

  • Used other than figuratively or idiomatically: see black, sheep. 

  • A worker who refuses to strike; a scab. 

  • A nonconformist; an unusual or unconventional person, who may be rejected or disdained by others for this reason. 

How often have the words bad apple and black sheep occurred in a corpus of books? (source: Google Ngram Viewer )