boff vs knock for a loop

boff

verb
  • To hit; to strike. 

  • to have sexual intercourse (with someone) 

noun
  • A great success; a hit. 

  • A pupil who works hard; a swot. 

  • A line in a film etc that elicits such a laugh. 

  • A big laugh. 

  • A hit or smack. 

knock for a loop

verb
  • To astonish; to stagger or overwhelm; to confuse or disorient. 

How often have the words boff and knock for a loop occurred in a corpus of books? (source: Google Ngram Viewer )