damnfool switch (n.): Engineering / aerospace jargon. Damnfool switch is an alternate term for the Master Envelope Interlock Disable switch; i.e., that switch which disables the hardwired safety features preventing the pilot, sailing master, or other operators from commanding maneuvers or equipment operations known to cause damage to, or the potential destruction of, the vehicle. (See also: redlining.)
The damnfool switch acquired its sobriquet due to the near-universal consensus that not only would only a damn fool disable said interlocks in anything other than a dire and imminent emergency, but that most of the people who have disabled them under such circumstances were also damn fools at the time.
idiot light (n.): The warning light, usually located next to the Master Alarm indicator, that indicates that the damnfool switch has been engaged; so named because the illumination of the idiot light indicates that an idiot surely must be in command of the vehicle.
– A Star Traveler’s Dictionary