Can I take my brother's phone away for showing everybody my grades?
Why would you take his phone away?
It's a bad idea to show everybody your real grades
I understand, but its not right to take things away from people that isn't yours. You shouldn't try to start a fight with your brother.
It's my brother's phone and I have a right to take it away. I will be nice and return it later.
You have no right to actually take your brother's phone, and it would be considered theft. You shouldn't ever take anything that isn't yours, from anybody.