The Big Red Switch really was big and red
In this article on compatibility between the .NET Framework versions 1.1 and 2.0, there is a passing mention of a setting nicknamed the “Big Red Switch”.
The power switch on the original IBM PC really was big and red. Well, orange-red. Here’s a picture of the power switch on an IBM PC-AT. Decide for yourself what color it is.
In college, the hallway that led to the basement lab where most of the computer science students did their work had a big red switch, a pushbutton, labeled “Emergency power shutoff”. Nobody was sure whether it actually was hooked up to anything or was simply a joke, but nobody wanted to take the chance of finding out, either. I remember one evening some people were goofing off with a basketball, and somebody missed a pass, and the ball hit the wall dangerously close to the big red switch. They (and everybody in the lab) immediately realized what had almost happened, and the group sheepishly took their ball outside.
Some time later, the legend of the big red switch was ultimately resolved. The morning after a particularly bad rainstorm, one of my colleagues came into the computing center and explained that he had gone down to the computer lab the previous evening and found it flooded, with water still coming in. Realizing that electricity plus water equals danger, he went over to the big red switch and pushed it. And true to its label, it shut off the power to the lab and the central file server. We were all in awe that he got to push the big red button for a legitimate reason. An opportunity like that comes only once in a lifetime.