I have an mp3 player in my head. There is always a song stuck on repeat. Usually whatever was playing on the car stereo when I last turned it off. So I make sure it's a good song before I go for a bike ride.

It's hard enough to hear other cyclists, cars, etc. while I'm out riding, so I will not put anything in my ears.

If I see someone riding with earphones, even just one ear bud, I assume they are anti-social and don't care about the safety of those around them.

(Currently my internal mp3 player is playing "Bridge Burning" by Foo Fighters. Down crooked stairs and sideways glances...)