Ningstas are people who are both ninjas and gangstas. Just think of gangsters with a ninja mask and a ninja shirt with pants down to his knees rapping.
A terrible, horrendous mistake of great proportion. Usually pertains to mistakes involving theft, rape, murder, failing in all academic endevours, and basically anything that is not defined as white-collar crime (no pun intended). Comes from the latin words "niggimus mistakumus".
After raping his third girlfriend of the week, D'Mario exclaimed, "I dun made me too many nigstakes this week".