How should I ruin his ego/reputation?

Call 911.

Call the cops and inform them of his abuse.

Never mind focussing on ruining his reputation. You need to look after yourself and any siblings that are left in the house. First thing you need to do is tell your friend's parents. Most parents will readily help out thier kid's buddies. Next you need to contact police or call the hotline for abused children (1-800-4 - A - CHILD) and they can help you find good resources in your area. You should also get checked by a doctor. You will need to detail what exactly he did to you this time and any times in the past. Be prepared, many doctors and emergency rooms will want you to have photos taken of any bruises or signs of abuse. If you have siblings, you need to be honest with police about what he's doing to them. If he is also abusing your mother, don't be surprised if she initially takes his side. She will likely be in fear for her safety or even her life, but with time and help, you can all get away and live peacefully. Remember, no one, NOT ANYONE has the right to put their hands on you. You have a basic right to feel safe. Please feel free to contact me directly if you need more in depth help or advice.

There are many people out here that care.

thats more than an ego problem, what he's doing is violent and abusive. you are within your rights to inform the authorities of the abuse that is going on in your house. he is in the wrong, no one should have to deal with that. instead of looking at it like your ruining his ego and rep, look at it like your getting justice and people like him need to be locked up!

I agree. Call the cops if you are worried it might happen again. Just plain getting even brings you down to his level. If you call the cops and bring in assault charges, this may not happen again. I would also get a restraining order.