little brother's disease Share definition Flag usually the middle child in a family who is trying to show up his older sibling. "damn Tyrone, Drew got that {little brother's disease}! Why he always gotta be up in the mix? little brother's disease by infidellicswaggernaut May 30, 2016 0 0 Get merch Get the little brother's disease mug. Buy Now — $32.95 See more merch