As you may recall, it was kind of a big deal last year when it was revealed that the then-new iPhone 6 would bend under mere pocket-level pressures. Naturally, now that the new, improved, metallic iPhone 6S has been released, people like JerryRigEverything want to test it again (this time against a box cutter and fire as well). I have to say, the flame test is actually pretty impressive. I did not think the iPhone would just recover from being burned like that:

Long story short, the keys and coins in your pocket won't scratch your phone, but you probably shouldn't carry open box cutters in your pocket. That's good advice in general, I think. Oh, or sandpaper. The phone will bend, but it looks like you need to apply enough force that you'd have to be determined to kill the phone anyway. Once things have escalated with Siri to that extent, there's nothing the designers in Cupertino can do.