Fetal McBrain Share definition Flag Premature brainulac tissue; a name to call someone at a random time. Also see feces. Zaquito, why did you steal my matzos and peanut butter?! You're such a fetal mcbrain nugget! Fetal McBrain by NuggetMcNug October 19, 2006 0 0 Get merch Get the Fetal McBrain mug. Buy Now — $32.95 See more merch