There is an old Native American tale, in which they were thought to be "immune" to poison oak/ivy. It turns out that they were just not prone to the rash. The Europeans were breaking out all over the place and when they asked the Native Americans how to become "immune", they were told to make a tea out of it :D...

Yeah, that really worked! How about death instead...

This was about the time when Native Americans were not happy with the Europeans.

No one is immune, some of us can tolerate it a bit more, but successive exposures will break down the tolerance.