Means your on my good side, your doing well, when being used positively. The negative definition would be used to shut someone up cause they are being rude, or a no thank you gesture. Can be used either way depending on tone and context.
When your trying to get to know a girl and she decides everything just might happen to be going perfectly, she will hint and say Ur Good. Someone says something rude like Hey lets go do the nasty and dont know you, so you reply nah Ur Good
by BabyHerc August 11, 2011