A contest, usually involving 12-14 year old boys, to determine who, among them, can cum the quickest. Sometimes involving as many as a dozen guys, ding ding can also just be a contest between two. This is one of the most common puberty-age, self-asteem building exercises among males. It is thought, at that age, that the ability to jerk off and bust a load extremely quickly, is a sign of maturity and sexual prowess, something to show off. The winner has to shout "ding ding" to prove that he indeed won.
Mark and Dave were ferociously playing ding ding in Mark's bedroom, and just as Mark was about to win and shout out loud in pleasure, his mom knocked on the door to the room, causing both guys to cringe and go soft. Blue balls then ensued, particularly in the case of Mark. Because of the mishap with Mark's mom, Dave turned out cumming first and winning the game.