I've once started a small fire. I had a software-controlled voltage regulator connected to the printer port (it was for a high-voltage programmer for 8051 chips

I've once started a small fire. I had a software-controlled voltage regulator connected to the printer port (it was for a high-voltage programmer for 8051 chips) and I was writing a Linux driver for it. I accidentally put the chip in backwards... I ran the software and suddenly had a physical manifestation of lp0 on fire on my desk. ;)