Obligatory answer

The "maximum pain that can be perceived by a human" is very subjective and differs amongst humans. For example, someone who is a cook may be very used to accidentally slicing himself with a knife, while an MMA boxer might be used to being punched in various areas - slicing a cook may not cause as much pain to the cook as it would to the boxer, and punching the boxer might make him laugh compared to punching to cook. This makes your question completely opinion based.

In 1984, torture was customized to the recipient. For me, it may be another forced upgrade of Windows. Extended duration? Check. Deterrent? Check. The only question is whether my sanity has survived.

"the suicide plant" : Dendrocnide moroides

@Mazura - either beating a person with the suicide plant so that his backside will hurt for years or simply injecting them with the neurotoxin. Good idea.

@MedwedianPresident Just wondering, does the torture have to be limited to physical pain of a person? Would psychological damage be suitable for your ... great leader?

I'm using linux mint. It doesn't force upgrades.

3 hours is too long, Eventually the victims will just give up, they would probably just start to ignore the pain while waiting to die in tears.

You might want to read up some Culture neural laces. Quote on nefarious use here: freebookol.net/Excession/66.html

Water boarding with ghost pepper extract.

I must say, the purpose of torture isn't to inflict maximum physical pain, but to psychologically subdue the victim. The pain is the instrument here.

Finally a use case for youtube.com/user/JustinBieberVEVO

The sad case of Hisashi Ouchi comes to mind...

Can't remember the novel, but a lasting image that's stuck with me is a torture chamber with a man that had had every nonessential appendage removed and the majority of skin flayed from his remaining body. He was carefully kept alive by doctors and displayed prominently as a message to new inmates that the torture wouldn't stop until you were a permanently damaged wreck... Just a thought to explore.

This question and its answers are easily the scariest thing I have ever read anywhere on SE.

Please, please don't go into politics.

Lois Mcmaster Bujold's Mirror Dance has a sicko who tortures very creatively at the end of chapter 24, i don't want to spoil it for ppl who haven't read it, but man she wrote some truly twisted characters

What's the point of this? Since it's an execution, the victim won't be able to go around saying how painful it was, so it's wasted effort. You could just have actors pretending to be in pain for propaganda purposes.