In the following video a male darner is chasing another male out of its territory. Males usually do this by approaching their opponent from below and behind. They swoop down low, then rise up for the attack.
In this case, however, both dragonflies are speeding along close to the surface of the lake. As the attacking dragonfly gets closer, the intruder begins to take evasive action. The attacking dragonfly mirrors these moves, as it continues flying at high speed, but its wing tips hit the surface of the water. The graceful little dance it does to avoid an unintentional splash-dunk or cartwheel is what I call the splashdance.