An exclamation used equally in times of excitement and frustration, designed to cause a similar feeling in the one to whom it has been said, yet utterly failing to do so. Originally used in Jane Austen's 'Pride and Prejudice'
1) Anger: ie, upon finding out your husband has just told your daughter he will never speak to her again should she marry someone you feel is a suitable match: "Oh, Mr BENNET!"
2) Delight: ie, upon finding your daughter is going to marry one of the most eligible men in the country, although he may own the miserable half of Derbyshire: "Oh, Mr BENNET!"
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.