How to stop people from snooping around in all the apps on your iPhone

You know that uneasy feeling you get when you hand your phone over to someone else so they can see something? Perhaps you wanted to show them a video on YouTube or a few photos you snapped of something funny or interesting. Whatever the case, there's always that brief, awkward moment right as your phone passes for your hand to someone else's when you say to yourself, "please don't swipe too far in the Photos app" or "please don't go digging around in my phone." You might not even necessarily hav...