drop a bomb vs pinch one off

drop a bomb

verb
  • To release feces into a toilet; to defecate. 

  • To release noxious gas from the bowels: to fart. 

  • Used other than figuratively or idiomatically: see drop, bomb. 

pinch one off

verb
  • To defecate. 

How often have the words drop a bomb and pinch one off occurred in a corpus of books? (source: Google Ngram Viewer )