We have the same urban legend in the US about poison ivy, but I actually knew a kid who made the mistake.

Poison ivy is certainly nowhere near this description of gympie-gympie, but the persistent itch is certainly unrelenting enough to cause pretty severe distress. I got a small touch of it on my forearm one time. Didn't even know I had brushed up against the plant, so I didn't perform the recommended clean up. Just from absent mindedly scratching, I ended up spreading the oil over almost my entire forearm and onto my leg. I barely slept for two weeks.