title_body: Why are spirits typically 40% ABV?
upvoted_answer: There is indeed a EU Regulation No 110/2008 about "the definition, description, presentation, labelling and the protection of geographical indications of spirit drinks" which prescribes the minimal ABV for different spirits and it happens to be about 40%. 
  
  So
  
  
  the minimum alcoholic strength by volume of rum shall be 37,5 %.
  the minimum alcoholic strength by volume of whisky or whiskey shall be 40 %.
  the minimum alcoholic strength by volume of vodka shall be 37,5 %.
  with the exception of ‘Korn’, the minimum alcoholic strength by volume of grain spirit shall be 35 %.
  the minimum alcoholic strength by volume of wine spirit shall be 37,5 %.
  
  
  and some more.
  
  PS. The Vodka myth may be of interest for you too.