Apparently these phones bend quite easily, so don't apply too much pressure when grinding, and don't put in your back pocket and sit down!
Honestly I'm leaning towards keeping my 5S for a while, the size and the chance of this happening bother me quite a lot, I just hope the 5/5S form factor isn't discontinued in the future.
The videos of people bending them are quite interesting - does not seem to take too much pressure, and they don't spring back to shape...
I am actually considering to buy Iphone 6 plus to replace my Samsung Galaxy S4. First time to consider an Iphone for me. Whoops looks like I have to postpone it probably to Iphone 7 plus or Samsung Galaxy S6