

Unforgiveable implies that there can be no mistake about the negative side effects for even the dumbest among us before committing the act. Torture is about as intentionally cruel as it gets.
Some other suggestions here are frequently used under the umbrella of torture, for example, by the IDF.
I think normalizing anti-social behavior as a virtue is something to add on there too. We’re all supposed to be confident nuisances to impress each other based on popular trends, but if anyone acted that way to us, we’d be upset. When upset, we don’t think about our behavior; we think about revenge.