the rainbow dash cum jar is a reddit post that depicts a rainbow dash figurine submerged in a mason jar full of cum. the owner of the jar would frequently update the posts and show the cum that has been added. the jar was later accidentally boiled over a space heater, turning the liquid brown.
When a man ejaculates his semen from a distance into another individual's mouth. The individual receiving the semen is sometimes referred to as "the pot of gold" at the end of the Cum rainbow.
Justin positioned himself 2 meters away from Ryan, and with great precision, managed to ejaculate into Ryan's mouth. Justin had achieved a Cum Rainbow.
A common phrase on sites such as Derpibooru, e621, Rainbooru and Rule 34 that means wanting to impregnate the character Rainbow Dash from the series My Little Pony Friendship Is Magic.