Datura scares me to death.
While I was living in Amsterdam a friend decided to try datura and we had to baby-sit them for 72 hours. They were doing all of the bizarre things you hear about. Talking to people who ween't there, smoking non-existant joints, asking really strange questions. A bird flew past and the tripper asked 'when I close my eyese, why can the birds still see me?.
Never scary in terms of they were never volent, but disturbing that someone could be expeneincing such a totally different reality.
Petrol fume are commonly used in some African nations. People buy 1l of petrol, place it in a plastic bottle and huff it for hours at a time. I read it causes severe brain damage.
Ether also saounds pretty nasty. I read that when it was first discovered there were a number of fatalieties. People were soacking a piece of cloth in ether and then lying down with the cloth covering their faces.
Have you seen the BBC TV series 'Quacks'? One of the characters is John Snow, a dentist and the first man to test both ether and chloroform during surgery. Although fiction, it's based on fact and when he began trials, about half the patients died.
So good list and certainly things I would NEVER touch.
BTW mentioing datura. In some prisons it's been discovered that inmates are smoking IBS medications that contain tropine alkaloids... crazy!