bikini vs skivvies

bikini

noun
  • A brief two-piece bathing suit worn by girls and women, especially one that exposes the midriff and navel. 

  • A brief bathing suit worn by men. 

skivvies

noun
  • Underwear, particularly men′s underwear. 

How often have the words bikini and skivvies occurred in a corpus of books? (source: Google Ngram Viewer )