The way you talk to your little brother is the version of you with no reputation to protect.

At school you are managing how you come across. At home with a younger sibling there is no audience and no cost, so whatever comes out is closer to the raw setting. That is why the tone you use there tells you more than the tone you use anywhere else. It does not mean you are secretly cruel, only that the filter is off.

Listen to yourself for one day at home. Notice the gap between how you answer a friend’s dumb question and how you answer his. Close some of that gap, even a little, and see what changes.