i have found that sanpaku Eyes is not just a superstition:

From all my travels, I've learned sanpaku eyes is not just a superstition. I have found that people with both combined (yin and yang sanpaku eyes) don't have it continuously, but when they want to make a point, or intimidate others. Those I have seen with both are very messed up in the head.

That's just my experience and I trust it. I don't judge or run for cover, but I consider them to be dangerous to my physical or mental well-being, or both. I flat don't trust them and that's that.