Evacuate!
Popping popcorn isn’t rocket science. Just follow the instructions on the box or popcorn bag. However, you really need a feel of your microwave, you know? This person used a strange microwave, the one in their office, and misjudged how much pop was going on.
Thankfully, the popcorn incident didn’t burn down the building. It did, however, produce enough smoke to trigger the smoke alarm, forcing everyone to sit around and wait in the 40-degree heat. Ironically, the office had just conducted a fire drill the week before, and the OP remembered clearly saying how “dumb” it was. You live, you make dumb mistakes, you learn.