A common nickname for the STD known as gonorrhea. People give this name to compare their spotty sack to Mr Tumble's spotty bag.
MrTumble'sspottybag is his bag which is a recurring weapon in the anime.
Person A: Do you have Mr Tumble's spotty bag?
Person B: Ew no gross... I use protection!
Person C: Lift your hand just like so.
Person A + B: Do you have Mr Tumble's spotty bag?
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.