I was surprised this year by a cockerel showing up in my sexed pullets. Naturally it had to be a RIR. I had heard the horror stories about RIR roos being the meanest of all the breeds, so I prepared myself for him to turn into a terror as he aged. He hasn't turned into a terror, but he isn't a great roo either. He is definitely human aggressive, and although he treads lightly around me for the most part, I wouldn't trust him as far as I can throw him (which from experience I can tell you is about 50 feet). He will likely end up as Sunday dinner because he cannot be trusted around people in general. I can't let the birds free-range when we have guests over and I can't let him out when my daughter is about because of his nasty sneak attacks. I think that some birds are simply never able to be trusted. RIRs are known to be some of the worst offenders.
Try to rehabilitate him if you want, but don't be too hard on yourself if you can't. You wouldn't be the first to try and fail.
Good luck with him.