I think this one in particular ticks me off personally because people I meet are all moralistic about me listening to podcasts while bicycling in traffic, telling me I "shouldn't block the sounds of the environment."
And I'm left wondering: have these people ever been in a modern car? Just sitting in it blocks out more of the environment than my open-backed earbuds. If I can drive one of those without causing an accident, surely I can listen to podcasts on my (much slower) bicycle without causing an accident too!