(noun) Derivative of "nitpicker"
In poker, refers to a person who is obsessed with following the rules, even when it will not affect the outcome of the hand. This person will hold up the game by calling for floorman rulings in obvious situations. Having a nit at the table is often detrimental to the spirit and quality of the table. Often a trait of a rock.
This nit on my right is going to scare away the drunk fish by harrassing him over every minor rule he breaks!