No, there isn't. However, as you hand the phone to someone else, hit the shutter button and take a picture of the floor or whatever. If they question you about it and you feel obligated to answer, just say, "How clumsy of me!"
You can also submit a feature request to Apple here:
Product Feedback - Apple
My additional advice is, if you make a habit of handing your unlocked phone to other people, don't keep pictures you wouldn't want them to see on it. It only takes a second for someone to go from the Camera to Photos.