Headphones Are Not Speakers

I was aboard a tram this afternoon and one of my fellow passengers had their hip-hop music blaring through their headphones. Surely the point of headphones is to allow individuals to enjoy their favorite music without disturbing other people and to contain that music between the listeners own ears. If they want others to hear, they should invest in speakers ( or a boom box)and then do the courteous thing of asking if anyone else would like to listen.