This is a great idea - although I am not sure what the response would be. I am not sure I would add a subtext just because, well, where do you start? lol It would have to be a sub essay!
If you are feeling confident enough maybe you should start simple and focus on letting people know about what it is and not primarily focusing on the "why they are wrong" thing. I have found my conversations with people are a lot more open and thought provoking when I take a more passive stance - especially here in the UK.
I think you can pick up horns online and they aren't too expensive. Just remember that to start a convo that is going to be fruitful you might want to make yourself appear normal
Maybe get a horn and use it as a demonstration purposes - but I would advise against dressing like Michael Rood and blowing it at people for example