My brother asks me to buy him stuff

I went up to the shop but before that my brother asked me to buy him some Coca-Cola and I said no

So he decided to harass me by asking so many times that he became pretty demanding

I told him No and walked out. I came back and he asked me did I buy him the thing he wanted and. I said no

He asked me why four times

This happens often and I hate staying off college for a day because of him