Treading in black waters means you are fighting or argueing with someone and you are JUST on the verge of telling them to fuck off. You can only use this term when you are about to end an arguement or a friendship/agreement. Should be used if you are completley ready to lose this persons trust and affection.
After James starting being a smartass and splitting hairs with me about how the server operated, I warned him he was treading in black waters.
It is said of the situation where a person has the bad luck to make contact with his testicles against an undefined surface or object, intentioned or not.
Given the nature of the word, it is more appropriate to design cases where the interaction is made with a moving object, for example, a ball.
Although it is extremely painful for the victim, it tends to be considerably funny to people who witness it.
Today in the baseball game the pitcher took a nutshot; the baseball hit him in the nuts.
Man, I just watched the funniest nutshot video ever.