I had a scary one about 20 years ago..
I was up on a lighting truss, focusing lights for an outdoor show, when I noticed that the L5-20C connector that I'm about to crawl over isn't clamped properly, and that whoever assembled it had stripped all three conductors all the way back to the cable jacket.. twisting that connector on the cable would have caused some nice fireworks.. it turned out that the other end of that cable was exactly the same..
I saw that connector, froze, and called down to the lighting designer, and told him to pull the main disco for the dimmer rack, since I'm 20' in the air, up on a grounded metal truss, at night, with dew on everything..
Another time, I was in a projection booth, and noticed that when they had removed the old amp racks, the crew had cut the SJO cable feeding the plugstrips in the old racks, but had not bothered to kill the breakers feeding them.. 3 live phases just lying there on the floor..