look up carotid artery and femoral artery. Either of those could do it quick. The femoral artery is my backup. I used to be a butcher. I know very well what it takes to cut deep and solid. I know how to sharpen knives well. Honestly, without that knowledge, I really wouldn't recommend it. You are more likely to hurt yourself and not hit something vital.
If you are going to do this, practice.
No joke. Get bone in chicken breasts and thighs or wings. Cut through them. All the way. Bone and all. You wont have bone for either of these spots, but you do need to overestimate what it will take to actually pull it off.
Then get some sort of large roast, preferably beef. Humans feel more like pork (so Ive read) beef is tougher. Again, over estimating. Get used to slicing very deep into said cut of meat. Brisket, rump roast, sirloin, those would all give a similar feel.
You don't want to stab. That is using a relatively small point to puncture a very large surface. sure you might get it, but your flesh might collapse in on top and slow it or you might miss. You want to slice. You need to slice deep. very deep. In the darker parts of the interwebs, (Im not going to search this at work) you can find people that bleed out or at least start to from their femoral artery. Think about what caused the wound. How deep did it have to go to get in there. I saw a javelin from some track and field thing do it to a guy once. went straight in his leg, he pulled it out, blood sprayed everywhere. It was a thrown javelin with all the force that carries straight into the thigh. Its hard.
Then you have to consider the effects. Survival instinct is a bitch and it is real. If you go for the neck, you are very quickly going to get dizzy while blood is spurting from somewhere you can't see. I imagine your kidneys will go into overdrive and kick you into panic quick.
Your leg, you are going to get sleepy more slowly. This isn't the blood bound straight for your brain. Sleepiness will happen over time and gradually.
Thats a personal decision for what you think you could beat better. Personally, I think the leg. Feeling breathless nearly instantly while breathing (if you don't puncture your trachea on accident) isn't my cup of tea. The leg though, I would panic and try to contain the spray to not make a mess. The adrenaline will hit and spike the blood pressure causing it to go faster. Survival instinct kicks in and you try to stop it, but you can't do it alone.
I don't know. They are both pretty hard. But once I figured out how hard it was to OD with normal prescription drugs, the femoral artery became my plan. Take lots of sleepers and melatonin. Lock the door. make the cut. Get your hands super messy so you physically can't unlock the door if you tried.
Takes huge willpower to watch yourself bleed out and not stop it and not panic. The cut itself will hurt, yes, but if you sit funny on your leg first, it numbs and that will help. Really I'd go with CO. 50 - 80 bucks for set up depending on what you have. Then you just go to sleep by a homemade fireplace and don't wake up. Less trauma on the way out. Less mess for those that are left.
Arterial spray is massive. No matter what you do, it will be a HUGE mess for whoever gets to clean up after you.
Good luck. Really, I think you can look through post history. I've talked about the CO method a few times. Here is the one I'm thinking of that had links in it to materials.
Good luck and be well. Whatever well is to you.