I killed a seagull with a kayak paddle once.
Ah, got it, MichaelEmouse.
As for me, I don’t care to make a list; it would be way too depressing. Highlights include a squirrel I hit with my car and sent cartwheeling off into a ditch, a beloved and long-lived goldfish who I put in a new tank which I apparently didn’t rinse well enough after cleaning, and innumerable worms I chopped up with scissors to feed to the snake-necked turtles.
RIP, all y’all.
With a question that broad, who hasn’t. I mean, I’ve been known to use soaps and hand sanitizers that advertize their ability to kill 99.9% (or some such) of bacteria. I imagine most people on here have done at least that much. I’ve also plucked a variety of plants from the ground, thus sentencing them to starvation, deprived of the soil’s nutrients. Again, I imagine that’s a very common experience.
If you’re looking at the animal kindom exclusively, I’ve crushed more bugs than I care to think about, though I usually try not to unless I have a good reason. I once set a trap that snapped the neck of a mouse. I’m pretty sure I’ve run over at least one squirrel with my car. While I worked in a dining hall, I placed dozens of live lobsters in pots of boiling water or boxes of scalding steam.
I once found a half flayed mouse that a cat had caught and then got bored with, the poor thing was still alive so I gave it the 'brick ‘o mercy.’ Gross, but instantaneous if your aim is good (my aim, thankfully, was good). I think that’s the only time I’ve ever intentionally killed an animal bigger than an insect or maybe bait worm/fish, though of course I’ve contributed to the death of a lot of cows/chickens and other food animals.
Yep. Cats. Deer. Groundhogs. Fish…
Like Phil Connors did?
Shot a squirrel when I was 13 with a .22. My Dad liked to go hunting and he thought that this time he’d take me with him, I guess to prove I was a man, or something. Maybe the one time he walked in on me masturbating didn’t convince him.
Anyway, I felt the guilt for a very long time and never went hunting with him again. My brother filled that vacancy.
Then another time, I hit a squirrel with my car as me and my girlfriend were out cruising. I knew I’d killed him and kept going. That’s when she started: “Bill Craig!!! You profess your love for animals and you won’t go back and check to see if that little one is still alive!!!” I took her home shortly thereafter and the relationship was kinda on the rocks after that. And yes, I felt guilty for not stopping.
Q
Of course: I’m not Ghandi. Bugs, mice, birds, fish. Indirectly: cows, pigs, sheep, lamb, chickens, vegetables, fruits; you know…food.
Did my best to kill some people in Vietnam.
Shot lots of deer, elk, antelope, rabbits, etc - all of which I ate
Bugs, a few mice with traps, eaten various plants, innumerable microbes.
You ran over a lobster with your car? That's....awesome. :)
Brushing your teeth? Hell, your immune system is practically bloodthirsty. Even then, I’m sure your stomach acid has killed at least one bacteria.
Ran over a cat once too. 
Innumerable bugs. Hit a raccoon in my car, that about did me in. Hit a black snake in the car.
Are we counting the pets I have had to have euthanized?
Aside from bugs and other vermin, I’ve killed the fish I’ve caught so I could eat them. The ickiest was when I woke up one morning and went in the bathroom where I stepped on a mouse hiding under the bathmat. It was quick for the mouse, at least, but it was not a good start to the morning for me.
The most advanced life forms I’ve killed were two cats. Both mercy killings, using a .22 firearm.
I’ve killed a lot of animals because I’m a life long hunter and fisherman.
I almost don’t feel comfortable putting in the same post as the above, but I’ve also had to kill people.
Everything that lives does so on the lives of other things.
So it is kind of a silly question. Either that or it is meant to weed out a certain type of person.
I once shot a man just for snoring.
Other than that I have trouble even killing insects. I find it unbearable to take another life, yet I’ll eat the hell out of some meat. And I like the smell of leather.
In the “with my bare hands” category excluding insects: I gassed a mouse caught in a glue trap when I was about ten. Then twenty years went by, and we got laying hens. One of our pullets ended up having a problem with her legs when she was about 12 weeks old, and had to be culled. Did the whole slit-the-neck thing, which was pretty difficult, but had to be done. In a couple of weeks, we’re getting our first batch of meat chickens, which will lead happy, healthy, free-range lives, and then we will butcher them when they are 8 weeks old. Not looking forward to that, but at least our meat will be ethically obtained, and not cost $25 a chicken like it does at the farmers’ market.