add insult to injury vs hit on

add insult to injury

verb
  • To further a loss with mockery or indignity; to worsen an already unfavourable situation. 

hit on

verb
  • To discover, pinpoint; to think up; to realize. 

  • To flirt with; to approach and speak to (someone), seeking romance, love, sex, etc. 

How often have the words add insult to injury and hit on occurred in a corpus of books? (source: Google Ngram Viewer )