Interpretations:I Wanna Rock

The joke is the different meaning of the sentence "I wanna rock!" The word "Wanna" is short for both "want a" and "want to" and the word "Rock" is a homonym for a name of a mineral substance, moving something gently (like a baby cradle), or making music. Which is the reason why the person threw a rock at the singer. Not for an act of hatred, but because when the singer said "I wanna rock!", the person must have thought the singer meant "I want a rock" instead of "I want to rock".