recurrent intense sexual fantasies, urges, or behaviors involving real acts in which another person is suffering psychological or physical suffering, pain, and humiliation. The victim's suffering, pain, and humiliation cause the person with sexual sadism to become aroused. The fantasies, urges, or behaviors must be present for at least six months.
Read more: http://www.minddisorders.com/Py-Z/Sexual-sadism.html#ixzz2Wgu7NoTR