Why should i share my food if i havent eaten all day when youve already eaten?

I came home with mcdonalds and this is the first food I've eaten all day long.its past 9pm here. My mom wanted some fries so I sighed deeply and now shes all mad at me and I have an attitude. Why should I give you fries. You and dad ate dinner already I'm about ready to drop from hunger why do i have to share