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.

http://youtu.be/QnPk4RRWjic