so-and-so vs whatchacallit

so-and-so

noun
  • Some thing or things. 

  • Used in place of epithets such as SOB, bastard, etc.. 

  • A placeholder name for a person or thing, used when a name is not known; a generic name. 

whatchacallit

noun
  • a whatchamacallit 

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