Not wearing headphones when listening to something in public is definitely inconsiderate enough to make you a worst person ever. I take public transportation to and from work every day, and I encounter this at least once a week. It drives me crazy. Train time is my quiet time and I can’t stand it when people interfere.
Also, have you ever noticed that it’s always crappy music that gets blasted and never anything good? It’s doubly vexing. Not only do I have to listen to what you’ve chosen to listen to, but what you’ve chosen to listen to sucks. Boo.