"Shaking S" is an Internet buzzword. It means "referring to a serious tendency to abuse others." This is a kind of character and psychological tendency, and it is also one of the cute attributes in the ACGN subculture.
"Dou M", an Internet buzzword. It means "a person who has a tendency to be sadistic". Just the opposite of S (sadistic tendency), it also refers to a personality and psychological tendency.
Source:
The original word "Masochism" in the word "M" comes from the name of Leopold von Sacher-Masoch, a nineteenth-century writer. His famous novel Venus in Furs also contains a lot of masochistic themes. The use of DouM comes from the M attribute "ドM", one of the cute attributes in the ACGN subculture in Japanese. Because it is pronounced as DouM, then this saying became popular.