I remember someone once said to me," Before learning a new language, one should get to know the vulgar worlds in the language." It sounds ridiculous to me back then. After all, I hardly even curse in my native language when I met the person. However, as I grew old, I realized that sometimes people curse to express feelings like fear, excitement, and anger. It is more of a spontaneously reaction other than wishing someone evil. Also, vulgar words sometimes also reflect its culture to some extent. Most importantly, everyone wants to understand when other people are saying bad things about themselves

That should be the biggest reasons why many people are eager to learn vulgar words.