Mine has a slight bend as well and I have honestly absolutely no idea how it happened. Never ever had any sort of damage to a phone, iPod, iPad in the past as I OCD in looking after my stuff. Was disappointed at the response I got from Apple Genius and subsequently the Apple store manager. They said that Apple policy is NOT to replace ANY iPhone 6 or 6 Plus with any sort of bend in it,. I was told to write to Apple in Ireland if I was still not happy. That was a complete waste of time as they eventually replied saying that my issue was a Technical Support one and that they did not provide technical support through written correspondence. My Letter clearly stated that I had been through the technical support route and that they had told me to contact Apple directly. All in all very disappointed.
As far as I am concerned the iPhone six plus has some sort of flaw that means in certain conditions it is susceptible to bending. They said it would have taken considerable force to bend an iPhone and my reply is if that is the case then surely I would be well aware of it happening.
I love Apple products though my recent iPhones and iMacs have not been as reliable as my previous products. I take great care of them and having spent many thousands of pound every year on Apple products I am very disappointed with the lack of support on this issue.
I anybody does know anyone who has had a bent iPhone 6 replaced then I would be very interested to know about it. Apple did say one of the places I was to seek help was on this forum.
Must say that, apart from the bend, I have had no other issues with my iPhone, and loving the camera especially.
Many thanks Iain