This was my first idea (extreme_bdsm) for it. But as @wat8548 pointed out, it's to subjective. And I accepted it... kind of.
My next logical step was to use the already existing, but barely used heavy_bondage tag. It took away the sado-maso part from bdsm. And left the being bound part. I would use the therm "heavy machinery" as an analogy, to explain why I used this tag. But well... after thinking about it, it's as objective as cute/cutesy/daww/wholesome.

I created the uncomfortable_pose tag. I think that's not that subjective. I added it to poses that seem... well... uncomfortable. Poses you can't endure for very long. I feel pretty confident using it.

Now to my attempt to get this cleaned up a little more. I was about to change most of the heavy_bondage tags to excessive_bondage_gear, but wasn't sure about it.
It would be used for scenarios like this, with lots of chains, ropes, and leather straps:
post #3164268 post #3188934 post #2912772 post #3219475

What do you think about it?