I sympathize with the hoards of urban dwellers who begrudgingly subject themselves to the purgatory of daily public transportation -- the screeching teenagers, sticky floors, and potpourri of smells are part of the reason I ride a bicycle. That said, there are things you can do to ease the pain of your commute.
First, don't look at anyone -- gawkers are universally creepy, so pick a spot on the ground and stare. Next, source a pair of headphones using the following criteria as your buying guide: durable, compact, noise-isolating, and "closed-back," meaning they won't betray your privacy and leak your music to fellow commuters.
This list includes both circumaural (over-ear) and in-ear bud style headphones. Both styles are suitable for noise isolation, though you may prefer an active noise-canceling headphone if your ride is extra annoying. If not, an ear bud with a well-fitted tip (silicone or foam) can be just as effective to mute the world around you