When the male partner inserts his testicles into the female partner's anus with his penis simultaneously inserted into the vagina. This often creates a side effect known as "fecal testicles" which most men find discomforting.
"Dude, I totally got to eighth base last night."
"I wouldn't try eighth base because it makes your balls all shitty."
"I wouldn't try eighth base because it makes your balls all shitty."
by The Douche Monkey June 18, 2014
Get the eighth basemug.