Williams says he attempted to contact Apple about the bug; however, he did not receive a response.
Here's how it works:
1. Navigate to iCloud in Settings.
2. Select your account.
3. Change the password to an incorrect one then tap Done.
4. Tap OK when warned that it is the wrong password. Then tap Cancel.
5. Reselect your account.
6. Empty the description field and then press Done.
After following those steps, Find My iPhone is disabled.
MacRumors has been able to successfully replicate this bug on an iPhone and an iPad running iOS 7.0.4, but could not get it to work on a device running iOS 7.1, so the flaw will likely be fixed with the upcoming update.
Check out the video below for a demonstration.