First, thank you for asking.
When the rabbit screams, imho it is conscious.
I used the backside of my Glock army knife, most important is to hit the right spot. That would be the cross when you draw lines from eyes to opposing ears. Hit really hard, and if there is any doubt, several times. Practise with a plush animal, a piece of wood, whatever, since your other hand will be rather close holding the ears down, and two fingers pinning their shoulders.
I knee on the ground, bunny between my legs (feet crossed so they cant wiggle backwards), wait til they calm down, and bop them.
I think a crow bar (the ones I know) is too heavy, hard to bring it to the necessary speed and being accurate. A 3/4", 1ft long steel pipe would imho be better, I like the knive becaus its about 5mm broad square back easily broke the skull, has a good grip and the center of gravity is about where it hits the rabbit, a similar piece of flat steel would work too.
Hard to describe, but you see it instantly in their eyes when they are gone.
Now I use a selfmade captive bolt gun, big advantage is that I have all the time I need to aim, and there is less bloodshot meat.