Commuting disturbance

So I'm on my way home from work about to settle down to 20 mins of tranquillity and a guy walks onto the train, music blaring.

Why do people think its appropriate to play their dance/house/garage/hip hop (delete as appropriate) music without headphones, for all to hear. No mate, I do not want to hear your music!

The daily commute is supposed to be a time of peace, reflection and catching up on my sleep. However, more often than not, it is disturbed by the youth of today who think I do not have access to MTV and wish to hear their latest offerings live. I'm sure it's not just me. Looking around the train I can see others who are just has frustrated.

What can one do? You daren't say anything for fear of being knifed/attacked/beaten up/mugged (again delete as appropriate) because clearly someone who has no issue with 'blasting out the tunes' with no consideration of others, will have even less of an issue, giving you 'what for' if you challenge them.

I dunno what do people think? What would you do?