Passenger handling controls
Only did it once. Dumbest thing I ever did.
I was flying an airtest in an S58T. I had an engineer in the left hand seat. He assured me he had had 'hands on' many times in his career. I let him handle the controls during a long descent. At 2000' I took control and increased power to level off. There was an alarming rotor droop and I discovered that he had wound off both twist-grip throttles, thinking it necessary for descent.
Lucky I had started to level off at 2000' and not 500.
Wrong to have done it in the first place but really dumb to assume that just because he was a type qualified engineer, he understood enough to fly it.