The unoffical rule of the internet that states, if it exists, there are ponies of it.
It is the pony form of rule 34, that states: if it exists, there is porn of it.
Brony 1: have you read the new starcraft crossover fanfic on equestria?
Brony 2: Wait, theres a starcraft/MLP crossover story?
Brony 1: Yeah, Rule P, makes it happen dude.