Classical music has a pretty precise definition of appropriate clothing, with variation allowed in various contexts. Metal probably has the second most precise definition of any genre, doesn't it? Rock is a bit looser, and then probably jazz, country, pop and hip-hop in that order? And indie pop probably dead last, because you can wear just about anything ironically.
I can imagine people complaining about what a rapper is wearing on stage, but complaining that it wasn't appropriate would be very, very rare.