Is my way of venting my anger bad?

My brother, who is six years older than me (I'm 18 and he's 24), likes to pick on me. When we have guests over, he doesn't do anything. However, every morning, when he wants me to do something for him, instead of waking me up at ask nicely, he likes to take a bucket of water from the bathroom sink, and dump it on my face.

When I refuse to do something for him, he gets mad and continuously hits me until I agree to help him. He's constantly looking through my facebook on my laptop when I'm not looking. He also likes to take my phone when I'm not paying attention, and text some of my female friends telling them I want to have sex with them.

This has been happening to me ever since my family moved to California from Taiwan when I was four. I tried to talking to my parents about it, and they've even seen him do such things right in front of them, but they won't do anything. It's even worse when one of my cousins comes over because my cousin always joins in on the "fun", as they call it. Whenever I ask them why they do it, they just tell me that "it's fun".

I don't tell any of my friends about it because they likely won't believe me. Whenever my friends are over, my brother hides his true personality away and acts nice to them.

A year ago, my brother bought a punching bag (I have no idea why), which I use, when he's not home. I found it a great way to vent out my anger and frustration at all of this. Is it bad the way I vent out my anger? Should I tell someone about my problems?