I have had Nankins, both SC and RC, for over 12 years. I have been gently pecked a few times when I put my hand too close to the baby chicks but I have not ever been attacked.
However, I also raise Delawares, and my ex-neighbors used to lure them over during their parties and then kick them. One of my roosters turned mean, and I have to remind him it's me when I open their pen, otherwise he gets pretty agitated. I believe that any chicken can be trained to be mean by a mean human.
There was some very interesting research in 2013 that says animals can inherit their parents' reactions to experiences -
https://www.smithsonianmag.com/smar...-certain-smells-from-their-parents-180948096/
So, if a bird has a bad or non-standard reaction to us, it may not be based on their experience of us, but rather that their parents or grandparents were not raised by someone who treated them with respect.
Also, Temple Grandin has some interesting comments about how the over-selection of a single traits (for example, color or size) can inadvertently lead to the extinction of other traits, like the gentlemanly behavior of roosters to their hens.
I have always selected for a good personality and parenting skills in my Nankins, but of course also looking at color and size, etc. I think we would all do well as responsible breeders to make a list of the traits we value and not ignore any of them. I am of course looking at this as a breeder, with generations at stake, and not as a hobbyist, with single birds at stake. So this may not apply to everyone.