I dont' know in place where you live. But in my country things of this kind are very very often. I really dislike animals like that, i feel very angry and very sad when i see something like this. Friend of my friend died similar way - guys beated him up because he didn't have some coins when they asked. He was a very good boy, does nothing except playing guitar and loving his girl.
I despite primitive morons like this, and i feel almost cry when see that - but also so angry that all moves and tehniques i ever knewed past through my head in second. I think there is no good punish for them except whole life hard work for nothing, in jail offcourse.
I had my experience to. I was going home from night party, and walk behind some disco. Minute later two guys run after me and aksed why i looked in them (i didnt't). After i stand in front of them and looked them they runed away (probably they saw i am ready to break them - when i see something like that i get enormous ability and wish to figth against that). But after 5 minutes they two run after me, + some six guys with them, one with basebaal bat. They didnt's say nothing, just started surrounding me. I reacted before they did it - i wouldn't make nothing circled with 8 people. I did something that i still think was it right thing. I striked closest guy in throat with SHIKANKEN strike tehnique - one i learned in ninjutsu, also known as very deadly move. While they stared at him falling down, i used that time for runaway..That was first time that i used something i learned in MA in real life, and still only time.
But my plan is not let some primitives to ruin or destroy my life. If that situation happens again, i will react the same.
Sorry for long text, but i just wanted to share my experience with you..
Greetings!!! Egon