As a one-time thing, I once did demonstrations of metalsmithing to a high school class in a room that was also used for ceramics. As I was demo'ing, I saw an 18 year old kid grind up some dried clay and snort it like it was cocaine. I stopped and explained that he needed to remember this moment... sometime in the not too distant future he would be diagnosed with silicosis, because what he just intentionally just snorted right into his lungs was a mix of talc, silica, and oxides. I then explained that silica was very finely ground glass. and if you looked at it under a microscope, it would look like jagged broken glass shards. And, there is no known way that it will ever leave your lungs once it's there, and the diagnosis is a death sentence.
He ran out of the room in a panic, and I had a conversation with the person in charge of the program. Apparently, I wasn't subtle enough in telling an idiot how stupid he is being.