pirates vs ninjas
A popular fight between two entirely different groups. Based on two different internet subcultures, Pirates and Ninjas, as two very different stereotypes battling out to death. May sometimes have robots, cowbows, or ghosts added to it. The phrase is also used as Ninjas vs Pirates.
One Piece Nerd: Pirates would totally win in a battle between Pirates vs Ninjas!

Naruto Nerd: No! Ninjas always win!