Is it safe for someone who doesn't react to poison ivy to eat the berries? I am not going to try it without authority from someone who knows. Is it like smoke from burning vines, that can affect even an immune person?
Your body just doesn't have a reaction on skin contact right now. However most people will develop a reaction after enough repeated exposure. While poison ivy doesn't bother me either, I do take basic precautions to not push my luck. With regular contact, you will develop an allergy, and though it could take years, it will take a lot less if you start eating the stuff.
The part of poison ivy that gets you is Urushiol. It's absorbed readily by the mucous membranes of the throat. If you eat the berries and develop a reaction you are potentially developing a reaction all throughout your throat, etc. If this happens, your throat will likely swell shut and... being miles from medical care... you'll die.
I doubt there has been any scientific study on how many times someone has to eat berries before they develop a fatal reaction (it'd be highly unethical).
Intentional ingestion of poison ivy berries is ludicrous. Knowing what you already know - why even dare to go there? If you are looking for attention getting or want free kicks to get off on you'd be better off playing in traffic. At least in that instance you would have a running head start to get yourself away from the danger. My advice is do not eat or ingest the berries. Worst case scenario is your heart and all other vital organs swell up and/or blister internally! Come to think of it poison ivy looks great from inside a cemetary plot.
Yes, they may be fatal! Is that a risk you're willing to take? As pointed out already even if you eat them once and you're ok, that may not be the case the next time.
If you're unsure of eating anything in particular in the wild I'd stay well away. With something that's known to be poisonous to a large number of people, it just seems silly to even try!
I actually ate poison ivy berries when I was a kid and I had no idea what they were, and nothing happened to me. I am immune to poison ivy and I don't know if that was a reaction to me eating the berries. They didn't taste good anyways, they tasted like they would be poisonous, super tart and green tasting left my mouth feeling like cotton. I remember my brother flipped out on me, but i just spit out what I didn't swallow and that was it. Nothing happened except I had to wash out my mouth a bunch to get the taste out.