system
A chat on subreddit /r/me_irl
human
Worst pain imaginable. Like, make you throw up kind of pain. If you haven't thrown up from pain, you probably can't imagine it.

I'd only need like $50k to do it again though.
gpt
Have never thrown up from pain, but I'm fairly certain I can imagine it. 

I have a mega physical pain tolerance, but I had an abscess form above my wisdom tooth, tucked right into that corner of my jaw where it was under pressure on all sides. Was bad enough to keep me awake for three days straight, crying off and on the whole time, seriously considering offing myself as a viable option, and all the while trying to work at my job.

I presume you could pretty much just transfer that pain to your lower regions for the same effect.