A Fortnite kid is when someone only plays one game and that game is Fortnite
kid1: Yo, whats up do you wanna play minecraft
kid2: Nahhhh i only play fortnite and im literally the best at it
kid3: kid2 you're the fucking worst at fortnite and play on a nintendo switch fucking brain damaged idiot
kid1: ok shitter go play ur game "fortnite kid"