[H1N1]

It is wise, with non-sporting violence, to always be aware of the position you occupy in the food chain. Unfortunately for you and your friend, you are in the same place most normal, healthy, well adjusted people are - more or less at the bottom. The best option open to you at the time was to remove yourself from a situation that might lead to physical confrontation. You didn't do that, and your friend got whacked for your sins. Rough luck on the bugger, but the way of it sometimes. Any thoughts of retaliation (even in my view extending the beef by getting them banned from places) are ill-advised, and likely to hurt you the most in the long term. The humiliation, guilt and rage you are probably feeling is normal, and an unfortunate and mercifully rare thing in most adult lives. In my opinion you should let this go entirely.