Booze. It almost killed me in my early teens with alcohol poisoning when like a dumbass I tried to drink an entire bottle of some cheap 'two fingers' tequila. And again around 2007 when I had to fight off a bunch of drunk gangbangers with my glock who were beating my friend and his girlfriend to death. Incident all started at a house party where some jealous drunk girl got mad at my friend's girl for disrespecting her but in reality she was jealous and mad because she looked better then her and her man took a peak. This simple act of drunkenness and jealousy escalated into a group of men encircling my friend and his girl and kicking and beating them with a bat and a fire poker. I almost had to murder multiple people in self-defense and I was shot at by some dumbass who's gun he probably never cleaned, jammed on him after his first shot went off above my head as he was trying to sneak up on me as I was trying to save my friends. Of course I heard the police arrived after the fact, great pro-gun story.
Meth could be up there as I have personally seen many lives destroyed by that and know of at least one person who was murdered for not paying his meth debt.
So booze and meth.
As for bad experiences for myself on drugs, other than booze none. I've never had a bad lsd or schroom trip, my experience with meth and other drugs like ketamine, pcp and ect were always short lived with no real bad incidents. Did a lot of good coke, and bad, never any issues other than small penis and heart pounding syndrome. Never like pills of any kind. Enjoyed different forms of hydromorphone, but never for long periods as the shit is so addicting. Anyone remember rush? lol Some dumbfucks sold that crap back when I was a kid. Just made you dizzy and sick. I can't think of anything bad happening to me except with booze. Oh, I did drink hard one-time, took some crappy lsd and did some good coke and that combo made me burn up. I was so hot I had to hose myself down in my friend's tub, but it passed and just turned into a drunken stupor. Now that I remember I did have the same 'hot' experiences with old school ecstasy in power form.