The thing that always tickled me was watching guys get on or off the huey in Nam and hunching over like the blade would take their head off
That's very much misunderstood. It's not the blades we are ducking, it's the wind and flying debris. It's a pretty strong instinct to duck down in high wind to protect your face and eyes, and to keep a low center of gravity to prevent losing your balance.
When a bird lands on sloping terrain, the blade tips can be at shoulder level. So we were trained to be wary and duck just in case.
