When I was just starting to get into drugs, I once bought like 40 10mg diazepam, then went home to crush them all up. I noticed my roommate had a script of bupropion, so I asked him if I could have it. So...I crushed up every one of those bupropion and mixed the two crushed powders in a baggy and shook it up. Did several lines, and on top of a sharp burning sensation that would make the devil himself cry, it made me feel worse than sober. We got rid of that whole bag of bullshit. What a terrific waste of Valium.
For a whole different reason: cocaine. I'm pretty sure that nearly every time I've ever done it, I immediately remembered why I don't do cocaine. Meth hurt too, but it hurt so good.