Yes, we have no bananas
Here is an example of a user interface that uses an "on/off" control on a negative assertion. In other words, "On" will "Disable" a feature. A control that uses "Enabled/Disabled" or "On/Off" and a positive assertion would have been simpler.
This bad UI design example comes from the AgileWP wordpress theme developed by someone with the handle "LiveMesh". You have to muddle through his logic to realize that "On" means "No".
It reminded me of the "Yes, we have no bananas" song.