"I had a work acquaintance, not close enough to be a friend, just someone I talked to once in a while. This happened more than 40 years ago... He tried cleaning it with bleach, and it had minimal effect. So he had some acid that he had brought home from work and dumped it into the toilet, which already had bleach in it. This released chlorine gas, which overwhelmed him. He barely managed to stagger out of the bathroom before collapsing..."