To describe a noun or pronoun that is as awesome as cats, which are clearly very awesome indeed.
Typically used to express one's appreciation after having witnessed an impressive display of skill, or to impress upon others the level of one's own skill.
Especially applicable to anything which involves a high degree of dexterity, mental focus and cat-like reflexes.
"Yo, did you see that Danny MacAskill bicycle trick video? Dude is mad catsome!"
"Shit yeah, I just got a 25 kill streak in Call of Duty! I'm wicked catsome!"
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.