"Rassclat" is a derivative of "Bumpaclat" and "Pussyclat", both of which are Jamaicanslang for menstral sanitary towels (Tampons and Pads). "Rassclat" can sometimes be shortened to "Rass".
"Rassclat" can be used as an adjective to disparage an object, but it is most often used as a highly offensiveinsult against a person.
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.