Well if you listen to music at insanely loud volume levels like many people at local meets do, then the noise leakage is a huge problem especially when you can hear someone else's music over your own headphones over the background chatter.
I also hate it when people let you listen to their headphones and they control the volume knob. Say the volume knob is at the 3 o'clock position:
Person: Is this too loud for you?
Me: Uh...hellz yeah it is! Tune it down back to 9 o'clock please.
Edited by miceblue - 9/7/13 at 3:51pm