Can be used in two different ways. One way being shock or surprise. The other way is more of a stubborn, selfpride thing meaning you refuse to do something, say something, believe something, etc.
Well, I'll be damned. Kenny fell in love with a hoe.
The veteran Confederates watch as the new VMI cadets hold their formation in the midst of murderous Yankee canon fire Veteran 1: I'll be damned.
Veteran 2: If I didn't see it with my own eyes...
This phrase was first started by southern Africans at the time of 17th century. People usually use it now when they see something that they thought was impossible, has been done. Or sometimes it can be used in a manner of not agreeing to something, in case of apologizing etc.
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.