Well, if you can't agree on what the terms mean then you can't have an actual discussion. It is what dictionaries are for, so we all know what words mean.
As an aside, there is no objectivity in the universe, everything is relative and subjective.
No, you see that's why a discussion has to be had. To make sure we are all in agreement with the terminology here. Even a dictionary's statement on things can be relatively vague, or even circular referring to itself. Even with what you just stated that somehow Objectivity doesn't exist and everything is subjective means that you referring to an objective measure here, being a Dictionary meaning, means that you are stating that you do not even believe that it is a valid statement because by your own words everything is subjective.
To note. I personally do believe in objectivity, but to be more precise, we define things objectively as something outside of ourselves to which we then measure something subjective.
In the case of our discussion about Sadism, we first agree on a basic objective element.
Sadism is a person who is sadistic.
So we confirm that objectively is true based on our language, while true that shared language is something we are subjectively using, it holds objective value in the existence of words and their meaning that we can somewhat play around with, but still maintain true to a core element.
And this core element is a person who is sadistic. So we move to Sadistic.
Sadistic would be someone who feels pleasure from inflicting pain unto others.
Now, I would direct you to one of my many questions in the wall of text about how to define that, how to classify that, and then what is real or false sadism. But ultimately those are what the dictionary has defined it as:
sadistic
/səˈdɪstɪk/
adjective
- Delighting in or feeling pleasure from the pain of others./
- Of behaviour which gives pleasure in the pain of others.
So we have something to measure it by, an objective measure outside of ourselves where we can now have a subjective debate about it on how we interpret and read this meaning and how we define each element of it.
Pleasure for example, does it need to be sexual in nature?
Pain for example, what happens when the person receiving the supposed pain feels pleasure instead? is it still pain?
If a sadist who enjoys causing pain to others actually causes pleasure to others, are they still sadist?
Again, you could be correct, but there are details to understand, complexities around what you stated that I am not saying you are fundamentally wrong about. But that brings about a lot more complexities and opens up things to widen the possibilities of what can be considered a "True" sadist.
To begin with, True is also difficult to evaluate here again, because it seems your argument is that it needs to be an unstoppable force for it to be true, while people who stop are not true according to you, or that is my assessment of what you stated.