The truth is, you would know if you were sadistic, as you would constantly be having thoughts about harming someone or those closest to you, who may be sadistic themselves and are always trying something on someone else and vice versa, it leads to a mishap of unfortunate unruly events which play out over a course of time and space. I know as I was the victim of such an attach, by one person I should add, as they thought fit to punish me in their own cruel way by submitting me to mental torture of bullying behind my back or in front of me. It was always the one person too, for several years this happened, and she usually had an accomplice with her. Tbh though, all my year group at school, seemed to have these gangs they had to constantly be in, or they would feel excluded from the school group.
Were they aware of what they were like and doing to others? yep, I think so. WHY? because I reckon they had enough spare time and energy at home to plot their revenge in their sad middle class extreme narcissism world with dressing down the victim for their obscene pleasures.
As well as all that, they would wind me up, but prey on my verbal difficulties, as I often found thinking in class quite difficult. I probably would have been a member too of their little soviet union if I had copied them and read their thoughts. I'm glad I could and still can think for myself as well as speak up for myself when need be.