Oh, yes, I have!
I had three hens. Two black-and-white speckled Plymouth Rocks, one Silkie Bantam. Their names...hehe...were...Lacy, Tracy, and Stacy. I know. So creative. Anyway! I had them for 4-H; I was going to compete with them and such. Sadly I couldn't register for that season in time, and, well, they didn't survive till the next...which is what I'm getting to, hehe!
I was pulling down hay in the barn and throwing it into a wheel barrow to spread in the pastures. I was, I wanna say, 12? Well, I'm throwing hay bales, when Lacy comes out from whoknowswhere...and I accidently throw a huge 50-pound hay bale at her. Lacy was the Silkie, you see...and she was like...3 pounds...so...yeah. She suffocated, I guess.
If I didn't feel bad already, I killed Tracy next. I'm pulling the wheelbarrow and squashed HER HEAD. Ew.
And then...Stacy... I believe she died of a concussion. Either that or she was suicidal. In the barn, next to all the hay bales, is this little drop down -- I don't know what it was supposed to be for, but it was never used. You have to climb down a ladder to get all the way down, and I was going into the little...cell. I figured Stacy wasn't stupid enough to come, right? Yeah. No. She's "balancing" on the ledge...and then...BAM! Hits the dust (ba dum dum).
So there is how...I killed my pet chickens, hehe.