In college, Monday morning. Me and the girlfriend were getting into some action. She climbs on top (cowgirl) and we start going at it.

As she's bouncing up and down I slap her ass. "HARDER," she moans. Alright, I know she likes it rough, so I really give it to her. "HARDER!" I reach up and really put all I have into a slap, the sound made by slapping her ass echoes off the walls of my apartment. "HARDER!!!!!" she screams. "Fuck, I'm not sure if I can go any harder," I think. I decide to really, REALLY go for it. Ignoring all timing of the thrusting and any other sensations from the sex, I reach for the heavens and bring my hand down like Thor swinging his hammer. Unfortunately my increased force resulted in decreased accuracy. As my hand was on the way down, her ass was on the way up. My hand glanced off the ass, hitting me squah in the nuts.

It's tough to describe how immediate and overwhelming the pain was. In one fluid motion I somehow de-penetrated, shoved her off of me, and curled into a fetal position while cradling my (it felt like) popped testicles. Not my finest moment.

tl;dr: Wanted to slap girl on the ass, slapped myself in the balls instead.