"抖S" (dou s) refers to a person who has a serious tendency to abuse other people. S is from sadism in the SM (sadomasochism). The key point of the words is "抖" (dou) which is similar to the degree word of tendency to something. It is a transliteration from the Japanese word "ド" which means "absolutely super". Similarly, "抖M" (dou M) refers to a person who has a very serious masochistic tendency, M is from Masochism.
Example: Xiao Ming has been broken up by his girlfriend, but he is still available on demand, serving tea and water, which is really "抖M" (dou M).