GI vs punching bag

GI

noun
  • One who is demanding and strict, in the manner of a stereotypical member of the military. 

  • A member of the U.S. military. 

verb
  • To clean aggressively. 

punching bag

noun
  • A person serving as an object of abuse. 

  • A tough bag, usually cylindrical, filled with air, sand, or other material, often suspended so that it swings freely, which is punched or kicked when practising sports such as boxing or martial arts. 

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