People with loud music carrying through their headphones is a pet hate of mine and many others.
I've taken to the closest you can get to London opprobrium for those who emit high levels of headphone leakage. A mean squint and direct eye contact. In terms of London discourse, I think the next step on the ladder is violent affray. I have regular fantasies about snip-snipping the headphone wires of offenders.
I've noticed more often than not that if I can hear headphone leakage then the wires are white. Meaning crappy Apple iPod headphones.
I've been told by someone in the know that the headphones are manufactured not by Apple but by some other well-known company - and it's really all their fault. So you say...
But I'll still be suing Apple when I go on iPod rage and really hurt somebody. (Oh, woman sitting next to me with your hip hop leakage last night on the Victoria line you came awful close. You're lucky that I only squinted at you and silently cursed you with a wish that you suffer long term hearing damage instead.)