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 latinwords "niggimus mistakumus".
After raping his third girlfriend of the week, D'Mario exclaimed, "I dun made me too many nigstakes this week".