When you're walking or something and your balls work their way so they're right underneath your ass. If someone looked at it from behind, you could see them just dangling there.

Also a very fun word to use to replace the nouns in a story.

Fecal remnants sticking to pubic hairs around anus; dingleberries; a general exclaimation of negativity.

Morbidly obese people with the appearance of two stomachs. One above the beltline and one below (the assballs area). Couple this with a tight pair of pants gives the stunning appearance of having an "ass" where the "balls" should be...Hence, assballs.
Assgina is this very same affliction, only in women.
Created by Skeets