At my office the big problem with popcorn is that the smell is distracting. It's a smell that carries very far, and everyone immediately recognizes it. Whether they like it or dislike it, it's extremely polarizing. So when one person has popcorn (or when the popcorn cart is started up again) everyone starts talking about it and we lose a lot of time discussing popcorn. Or going downstairs to get popcorn for ourselves, or what have you.
I have to admit, I was one of those people who caused a fire alarm to go off in college. To be fair, it was a personal sized bag of popcorn, but still said to leave it for the full 2:30, and I was using my suitemate's microwave, but she did NOT want me in her room while it was cooking. So I asked her to pay attention for me, as I was sure the time listed on the bag was wrong. Nope, within a few minutes the smoke alarms were going off and everyone was evacuated. I never trusted anyone else to watch my popcorn again, and I've never walked away from it.