An abbreviation for the phrase "Nigga stole my bike!" The phrase originates from a Something Awful photoshop edit of a screenshot from the
game Punch Out!! (particularly, a screenshot after a circuit) when Little
Mac is running with his coach who is riding a bike,
Mac is saying "Nigga Stole My Bike!" It became more famous from the site YTMND (www.ytmnd.com), where someone made a site containing the picture in question with a sound
clip of a black man saying the phrase.