This is why I walk to wherever I need to go. It would depend on how I felt that day, if I could tolerate his music, so I'd either shrug it off or casually ask him to turn it down. I might even give him a set of headphones so he could still hear it. If he did nothing, I'd badger him about it until I became more annoying than the music. If he still did nothing, I'd look him over and probably sit back down. I wouldn't hit him unless he touched me.
As far as seeing a bully, I'd firmly ask the person to stop. If they refused or started hitting me, I'd wail on the person until either they fell or I did. I've gotten very calm lately, and I try to not create violence in front of kids or old people, but I have zero tolerance for someone who violates my bodily security.