1 definition by lone sentry
Bike Ninjas are people who wear all black, and and become very ninja-looking when wearing a face mask / balaclava in cold weather. The all black also adds to their "invisibility" while riding at night (which can be dangerous). Bike Ninjas are often urban dwellers, ride fixed-gear or single-speed bikes, and are usually "hipsters" of some sort (hence the all black clothes).
"Some bikers wear all spandex, and others wear all black and look like Bike Ninjas."
by lone sentry Jan 8, 2012 add a video