Derived from RNG or Random Number Generator. Typically used in video games due to the luck of a random number generator being represented as a Miracle or Divine intervention and thus the character of RN Jesus is prayed to or thanked for Luck. Most situations where RN Jesus is invoked involve games with Random Criticals like Fire Emblem and Team Fortress 2.

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

Usually associated with video games,
RNJesus is the deity of RNG. (random number generators)

When the outcome of a certain scenario could be determined by a random factor most players can do nothing except pray to RNJesus.