I once as a prank stabbed my brother with a fork
Why would you stab your brother?
He laughed at me and I wanted to scare him for a second.
Your aggression could be something else that is buried deep inside of you. After you make amends with your brother, talk to someone about what's bothering you so this doesn't happen again.
It wasn't a big deal. I just did it since I'm bored and had nothing better to do.
I know you see it as just a prank, but it's still wrong to stab people even as a joke. What if you seriously hurt him by accident?