For me, the most difficult and frustrating thing was always the cross-legged, neutral buoyancy/hovering maneuver. I would repeatedly explain to them, that the tank's weight would cause them to tilt backwards a little, but that they weren't going to flip over or start doing back spins or anything, that all they had to do was relax and hold on to their fins, and expect to be to be tilted back a little. But almost without fail, as they tilted back, they'd spaz and let go of their fins, start flailing around trying to re-orient themselves vertically again, only to fail.....lather, rinse, repeat. I would even demonstrate myself, exaggerating the backward tilt to show how it would all balance out, while emphasizing holding onto the fins, then when they tried it, they'd invariably let go of the fins, and start flailing around trying to get back into an upright, seated position, that was never going to happen.
I'm getting annoyed just sitting here talking about it, LOL!!