The douchebags who have no notion whatsoever of "public space" and "annoying", and decide to use their cellphones or their mp3 players to listen to their music without headphones, which means that everyone will have no choice but to listen to their music. This one gets more painful because the sound is always too loud, and its quality is never good; and the music itself is the shittiest thing possible, sheer ear-killer dance music or hip-hop. Seriously. People with a decent musical taste also are decent enough to understand the value of headphones? Fucking hell. Everytime I find one of these assholes in a bus I can't help thinking "now a bullet between the eyes wouldn't really be wasted".