It's industrial-strength bleach. Literally just bleach. Usually drunk, sometimes injected, and yes, it often kills you. It is every bit as bad as it sounds if not worse.

Industrial strength bleach? Not even diluted? Sometimes injected? But that's a go to method for a cruel and painful but fairly quick way to murder someone!

My brain is still not pessimistic enough about human stupidity.

Likewise. In fact there aren't many people I would have believed at face value if they had told me this was actually a thing people do.