I either snap their necks or put them on the block and chop their heads off with an axe. First year I had chickens I couldn't face doing it, couldn't even watch it being done. It's something that you get desensitised to over time. First I watched a local slaughterman skin and gut one of our lambs that I'd bottle fed and kept indoors under a heat lamp when it was sick. I couldn't watch him killing it but I wanted to see it being gutted. Next time he came to slaughter another lamb I asked him to do one of my nasty roosters, and I made myself watch so I could learn how to do it. Next time one of my old hens prolapsed and needed euthanising urgently, I did it myself. Not nice, but I did it. I haven't killed anyone purely for food yet, but I will soon. I know most of my chickens as individuals, but only two of them have names. Giving them names makes it much harder IMO...