backstab vs pick on

backstab

verb
  • to attack someone (especially verbally) unfairly in a deceitful, underhand, or treacherous manner, especially when they're not present in the place or situation that it happens. (as if stabbing them in the back). See backbite. 

pick on

verb
  • To bully, harass, or make fun of a victim; to bother or harass. 

  • To select (a person) for a task, etc. 

How often have the words backstab and pick on occurred in a corpus of books? (source: Google Ngram Viewer )