my father once put a pizza box into the oven then turned the oven on to keep it warm, intending to turn it off quickly but forgot. Fire ensued
I was 18 in a terrible apartment and needed to run over to my buddies place to borrow something. I had stock on the stove but figured it had to reduce and I could go and be back quickly. We had one of those sandwiches that they have on How I Met Your Mother and I forgot all about the stock. The guy across the hall and I had swapped spare keys. He saw smoke pouring out of my kitchen window and let himself in and threw the pot in the sink and turned the water on. Crisis averted other than me thinking about it and being filled with shame every time I put a pot on a stove.