Emo's Favorite Music Element

Listen up, you chucklehead, you're about to learn something. You're clearly not the sharpest tool in the shed if you're asking about this. Emo is a subculture where people tend to be emotional and introspective, meaning they are preoccupied with themselves. The joke plays on the word "harmony," which in music is when different sounds combine well. Here, it's self harmony, implying they only care about their own feelings.