"Sex Feathers" are Neck Hackles and Saddle Hackles sometime just called Hackles and Saddle feathers...
Here is a link with some information that will help you identify Hackles and Saddle feathers... https://www.backyardchickens.com/forum/viewtopic.php?id=343605
thank you to all for convincing us of our lop-sided hatch - amazing. hey'll be heading out for the auction on Saturday. In case you were curious - our crower is charcoal. He came out of his egg like he was gonna show us something then already.