The act of two males either:

(1) engaging in double penetration while both are pumping hard at the same time so that their balls smash against each other every thrust or
(2) masterbate while facing each other, close enough to touch tips or plop, but instead they hold their manhood upward while stroking and simultaneously thrusting forward. Causing their hanging testicles to knock together mid-stroke.

When you eat dirt for the first time and leave your family to build a shack in the woods