But the crowning horror was what they were treating their fellow commuters to. It was not underground gangsta rap, as one might reasonably respect of a crew of tracksuited badasses; nor was it some major-label manufactured rap, as a bunch of suburban poseurs could get away with being into. It was boy-band R&B.
Perhaps that's some kind of peacock-tail phenomenon of conspicuously flaunting one's badness, as in "I'm such a mackdaddy that I can play utter crap and no-one will fuck with me". Or perhaps it's a mutant form of vandalism; the sonic equivalent of kicking out windows and tearing up seats.
* with apologies to the Doug Anthony Allstars.