Unfortunately, I'm pretty sure that adding something like that would make things worse and open the door to wasting your time on pointless issues like "Why are you using this code of conduct instead of $my_pet_code_of_conduct?", whereupon you tell them they're not working towards the project goal, which leads to even more drama. It's simply not worth it.

Those who can, do. Those who can't, open an issue about the code of conduct.