Ravot.....
An Idiot Mark is when you are reassembling the prettiest, smartest looking 1911 that you have ever seen and are in the process of reinstalling the slide stop pin. If you're not careful, you will pivot the pin back and forth while it's resting on the frame and will immediately install a very nice deep scratch in the form of an arc on your pride and joy. Do a search for "idiot mark" on some of the forums and you will see some beauties. According to OleCodger's law of physics, the nicer and more expensive the pistol, normally the deeper the mark.