There is a difference between happiness and pleasure and happiness requires no unhappiness to result in others. The only way a sadist can earn happiness is if they are only dealing with masochists and everyone is getting precisely what they want. But masochists do not want misery, they just enjoy the pain, which is as different from misery as happiness is from pleasure, though they may coincide.
Happiness is simply being happy (or, if you want, content and enjoying yourself).
If you do that by inflicting unhappiness, or by depriving others of things, etc, it's still happiness.
There's no part of the happiness definition that says it's incompatible to with "unhappiness to result in others". That might be part of Bhudism or Christianity etc, but it's not some given of human nature.
One can't be a Scotsman if one's ancestors don't come from Scotland.
There are things that are true because they fit the proper description and there are people who use "No True Scotsman" because they don't want to learn the truth.
