When you're working out and you get a hard-on so you jack off. After you cum, you clean yourself off and go back to working out.
"Hey Bro, I was halfway through gettin' swoll when a total babe walked by me."
"So what did you do?"
"I whipped out my raging hard cock and jerked out by the treadmills."
"Dude that's really messed up, I could never jerk out in public."