Is the bending issue a problem in iPhone 6 or just iPhone 6+?
If you apply enough force to an inch-thick solid steel rod, it will
  bend. 
  
  Same goes for the quarter-inch-thick iPhone 6 and 6 Plus (which, I
  should note, have far less than a quarter of an inch of aluminum in
  any one spot). 
  
  Aluminum is actually a fairly soft metal, ranking at 2.5-to-3 on the
  Mohs scale of hardness. 
  
  That is to say, it's about as tough as a U.S. penny (which is actually
  97.5% zinc and just plated in copper).


Source: http://www.imore.com/yes-aluminum-iphone-6-and-6-plus-can-be-bent-if-too-much-pressure-applied

I would not recommend to stick it in the back pocket of a very tight jeans, and then repeatedly sit on it.