Legal stabbing

I was out the other day with a friend who has a severe allergy, and as a result, carried an epipen. As we started to talk about it, I admitted I'm not sure I would have the guts to stab someone, even when I knew it would save their life. She said you muster the courage, and won't even think about it in the moment, you'll just stab them. And then we laughed a little. Might be the only time it's legal, and even encouraged to stab someone. 

"I'm sorry convulsing unresponsive stranger, I just don't know how I feel jabbing this needle into your leg...it's leg right?" I hope that isn't another wildly inaccurate fact Hollywood has made common knowledge. I carry chocolate around in my purse, just in case I meet a diabetic who needs it, but I hope they'd be with it enough to ask for it. I hope I could stab someone with an epipen should they go into anephalitc shock. If you hesitate, does another stranger force your arm down, or grab it out your hand and do it for you? Ah, this courage thing is tricky business...