What do you mean, "You must be M"?

The m here is short for Masochism, which means masochism.

Sm is short for sadistic masochism, especially in sex. Usually S is the abuser, M is the abused party, S is also called the master, and M is the slave. In other words, in SM, S is the abuser and master, and M is the abused and slave. SM is not only a sexual abuse relationship, but also a master-slave relationship. Sm is a special activity that sexual pleasure and pain are linked together, that is, sexual activity that obtains sexual pleasure through pain. SM is a kind of sexual perversion and belongs to one of the important terms of bdsm. Among them, pain includes both physical pain (such as the pain caused by flogging) and mental pain (such as the painful feeling caused by humiliation and domination). Sadism also includes two categories: sadism and masochism. Putting pain on others, you can get your own sexual pleasure, sexual excitement or simple pleasure, which belongs to the former, while accepting pain can get your own satisfaction, which belongs to the latter.

Word source:

The west calls it sadism &; Masochism (sm for short) refers to the consciousness and behavior related to sadism and abuse.

At that time, especially in Britain, which can be traced back to the whole Victorian era, a major trend of underground pornography was sadomasochism. The most obvious is the strong love of the British people for flogging at that time. Even today, flogging is still called a British vice in continental Europe.

In China, SM has a warmer name: Sadism. I think this name is wrong. SadoMasochism, a word in English, is a combination of Sadism and Masochism. Its abbreviation is what we usually call SM.