To focus on the activity in front of you and avoid all distractions; to "lock in" and get your work done.
When Doc Miller's students started fooling around in class, she told them to "get frosty," so they would start paying attention and get their work done.
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.