"Sadistic personality disorder is a pervasive pattern of cruel, demeaning, and aggressive behavior, beginning by early adulthood, as indicated by the repeated occurrence of at least four of the following:
* Has used physical cruelty or violence for the purpose of establishing dominance in a relationship (not merely to achieve some noninterpersonal goal, such as striking someone in order to rob him/her).
* Humiliates or demeans people in the presence of others.
* Has treated or disciplined someone under his/her control unusually harshly
* Is amused by, or takes pleasure in, the psychological or physical suffering of others (including animals).
* Has lied for the purpose of harming or inflicting pain on others (not merely to achieve some other goal).
* Gets other people to do what he/she wants by frightening them (through intimidation or even terror).
* Restricts the autonomy of people with whom he or she has a close relationship, e.g., will not let spouse leave the house unaccompanied or permit teenage daughter to attend social functions.
* Is fascinated by violence, weapons, injury, or torture.
The behavior has not been directed toward only one person (e.g., spouse, one child) and has not been solely for the purpose of sexual arousal (as in sexual sadism)." (information obtain from http://en.wikipedia.org/wiki/Sadistic_personality_disorder)

"Sadism refers to gratification in the infliction of pain or humiliation upon another person. Masochism refers to gratification from receiving the same.1Often interrelated, the practices are collectively known as sadomasochism as well as S&M or SM. These terms usually refer to consensual practices within the BDSM community." {http://en.wikipedia.org/wiki/Sadism_and_masochism}

this is a very complicated topic and i would advise you to read the links to understand it more http://en.wikipedia.org/wiki/Sadism_and_masochism

I believe a person's sexual arousal has to do with their own perspective of the taboo nature of a particular behavior. For example, I grew up in a household where smoking cigarettes and drinking was a big no-no. I never saw my parents drink or smoke ever the whole time I was growing up, so smoking and drinking became taboo for me. Once I grew up, the notion of smoking a cigarette was taboo to me and would bring about a type of sexual arousal in me (also known as smoking fetish).