knob-end vs shithead

knob-end

noun
  • A stupid or contemptible person 

  • Used other than figuratively or idiomatically: see knob, end. The end of something that is shaped into a knob. 

  • The glans penis 

shithead

noun
  • A stupid or contemptible person. 

  • A card game, the aim of which is to lose one's cards. 

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