I am a parent but I am not offended by your attitude towards yours. It sounds to me like you must have a good intuitive understanding of how to work with your rooster. Your parents do not, but this doesn't mean they are dumb. It means they lack knowledge on the subject. You have been trying to educate them, but perhaps not tactfully enough to make them want to listen, or perhaps they are simply not motivated to learn. If it's the latter, you cannot do anything about it. If the former, maybe you can adjust your style to make them more receptive to what you say. Approach them as respectfully as possible, and you might see better results.
It might help to ask them to read something about rooster behavior. Maybe it will be more acceptable and meaningful to them if the information comes from an "authority", rather than directly from their child
Here is some excellent information on rooster behavior to read yourself and suggest to your parents:
http://www.themodernhomestead.us/article/Cocks-1.html The second article, on rooster aggression towards people, will be of particular interest to you and your parents.
The fact that your rooster is tame with you says that he is capable of trusting people and behaving non-aggressively with people. So, there is an excellent chance that he will be able to be just as tame with your parents, provided they are interested in doing what it takes to show the rooster they pose no threat. This could take considerable time and effort on their part, though, and they simply might not have the time or interest. They will probably need to spend more time with him, be mindful of appearing non-threatening, offer him special food treats, etc.
It might also help your parents to learn why roosters are sometimes aggressive. That is, what advantage this behavior was to their wild ancestors. That might help them to not take his aggression personally. I think this is covered in the articles at the above link.
Of course, you might not be able to inspire your parents to do any of this, but do your very best, as tactfully and respectfully as you possibly can. You want them to respect your rooster, so model that respect in your communications with them. You might lose this rooster, but maybe you'll make some headway with them, and set the stage for a smoother process next time around with another rooster, or with some other animal.
By the way, I'll share a secret with you: I had exactly the same problem with my kids! I have a rooster, very tame with me, become aggressive with my kids. I could see that he was afraid of their quick, unpredictable movements, so I had to teach them to move more slowly and predictably around him, to generally be more aware and respectful of his needs, and eventually to hand feed him. He is much better with them now, but still somewhat suspicious. No more attacks, though. He'll briefly charge at them occasionally, but no attacks.
I think I had a much easier job, because I am the parent and can exert more control over my kids. You have a much more difficult task ahead of you!
Good luck!
