This link is exactly the sort of thing that I try not to look at, but can't leave alone, once I see it. It's disturbing. It's also the sort of thing I prefer not to read, but sometimes do. Sometimes it's by accident, and as soon as someone starts cutting someone else's nipples off, I navigate back and look for something else. Sometimes the one being de-nippled is also screaming in orgasm, and I have to roll my eyes at the over-the-top fantasy. Sometimes I keep reading, just to see how far the author wants to take it, or to see how much of it I can stand.
Interestingly, I always try to understand what causes this to be arousing. I imagine getting aroused at these stories or images, and the only conclusion I reach is that it's exciting to cut loose from one's human empathy--it's like going in public without clothes; thousands of years of culture (and physical necessity) has trained us to wear clothes, but it's exciting to thwart that culture sometimes.
Or maybe it's the pain, screaming, and blood. I find that harder to understand.
Now, all of that has little to do with this: another story code, well-intentioned as it may be, won't do much good for this site. We already have a "violent" code, which can mean anything from a good hard spanking to the aforementioned nipple amputation. There is also "modification," which can mean a sexy clit ring or a sci-fi pain delivery device implanted in body tissue. I love the story codes for a quick snapshot of what lies ahead, but they're not 100% reliable. I think that even with the added code you propose, you would still stumble upon stories you find offensive, and you might pass over milder stories that are not as "extreme" as the author imagines. I've found that the best way to find the "good ones" is to remember the authors of the ones you like and ask for recommendations on the forums.