I was just thinking to myself the other day… What could you inject into somebody that will cause the most agonizing, horrible, gruesome way to die, under a week? It has to be a liquid that you can injet into someone via an IV type needle. Some kind of acid? Something that will slowly freeze your blood, cause it to expand until you blow up?
thoughts?
Need answer fast? 
Injecting an acetaminophen (paracetamol) solution of sufficient concentration will result in a slow, painful, agonizing death from liver failure.
A combination of blowfish toxin with jellyfish and spider venom?
Paralyze them so they can only lay there and “enjoy” it.
Air
Poisonous lava
Clamato
Hydrofluoric Acid
It’d probably take longer than a week.
JB Weld
Years ago a local motorcycle organization near here shot some guy up with a bunch of battery acid.
This was after they shot and stabbed him several times but before they dumped him into a quarry.
The dude lived!
I don’t know if this is an indication of a tougher constitution than most people have or that battery acid isn’t the best thing to use for your situation.
potassium chloride
I’d go with a big, cloudy vial of methicillin-resistant Staph. aureus or meningococcus.
Yes, as a matter of fact I am terrified of sepsis, necrosis, gangrene, etc.
Liquid Mercury?
You needn’t bother injecting this, though - hydrofluoric acid is readily absorbed through the skin. Just douse a sufficient portion of the victim’s exposed skin in the stuff. A slow, agonizing death will ensue.
Oh, I forgot, since we’re looking for painful, I was thinking this would be even more painful if it was inject IM. It might not ‘absorb’ but I think it would hurt like hell tearing the muscle apart as it goes in.
Anyone read The Diamond Age by Neal Stephenson? (great book, btw). There’s a method of execution described called the “seven minute special”, or something like that. Basically you’re injected with a bunch of tiny little nano-bombs, give them a few minutes to course through your veins and get all spread out, and then when they flip the switch, you basically explode all over the place.
My vote is for some methicillin and vancomycin resistant staph aureus in solution. That’ll fuck you up until they find out what it is, and by that time it’s probably too late.
They explode in a spherical pattern. When it’s done, you look like you’ve been cut down by a melon baller, or like the net of dough that’s left over after you’ve cut out all the cookies.
But significantly less appetizing.