Peabrain Share definition Flag An unfortunate, clumsy, dim-witted, accident prone individual whose many faults can all be attributed to their pea-sized brain. "You're always knocking things over you stupid, stupid peabrain" Peabrain by peebrayn November 22, 2011 0 0 Get merch Get the Peabrain mug. Buy Now — $32.95 See more merch