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.
Argh, stupid NSMB ytmnds, there's so many..
Nigga stole my bike!!!!
You are ridin down the street and a nigga beats you and steals your bike you say NSMB!!
New Super Mario Brothers
NSMB is the best 2d platformer for the DS!