A home gym setup, generally used by cyclists, but also popular with other disciplines. It refers to a dedicated area, generally in a basement (hence, "cave") where long, grueling exercise sessions take place.
I did a triathlon in May, which meant lots of long days in the Pain Cave, since it was too cold to train outside.
A mentally and/or physically debilitating condition worse than a hang over usually brought on by the consumption of copious amounts of alcohol combined with severe lack of sleep.
... oh my head... it's a day in the paincave for me today, thanks to that goddamn moonshine!
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.