A year or two ago, I was giving a lecture at a medical convention in Los Vegas at one of the big hotels. I arrived about 45 minutes early, hooked up my laptop to the projector, turned everything on and made sure all the electronics were working and I could show my slides. I have been doing this for decades; as a good risk manager, I like to start on time and make sure any problems are resolved before showtime.
Some guy came in 15 minutes before the start of the lecture, saw that I was good to go, and started reaming me out: he was from the union, and only they were allowed to touch or set up any audio-visual equipment. I had no idea. He threatened to unplug and take away the projector unless I apologized. I did so and he went away in a huff.