I've had to euthanize one chick and then I have also processed one rooster. For the chick who, unfortunately, developed a severe crossed beak, I couldn't do it as while caring for her I grew too attached. My husband grudgingly did the deed for me and to this day will not tell me how he did it.
As for the rooster, he had gotten too aggressive with the hens and was huge. He was not the lead roo and I just got exhausted with hearing all of the squawking of the hens and of the lead roo disciplining him.... Soooo, I got my courage up, went and purchased a large traffic cone from Home Depot. Cut the top off of it to make the hole larger. Hung it upside down, placed Mr. Roo into it with his head coming out of the bottom. He took this all very calmly. I then made short deep cuts on either side of his neck. He did not react in pain to this. He bled out very quickly. Of course, there was a small amount of spasms but at that time he had already expired.
I almost talked myself into throwing him away, but that just seemed wasteful and disrespectful. So I skinned him and a couple of weeks later, I wrapped him in bacon, put him in the oven and invited my parents for dinner. He was yummy and best of all, it's much quieter around here, the hens are much happier and I don't have to stress over it anymore.
I think it's much easier when it's a mean rooster causing havoc than when it's a helpless chick or sick hen. But I think now that I have done the rooster, it will be a tiny bit easier for me to cull due to illness or infirmity. The chicks though, I think will always be very very hard
. This is the method I was most comfortable with after extensive research and watching numerous videos. I think it just takes finding the particular method that fits your comfort level while taking into consideration the welfare of the bird.