Human Factor, sorry for trying to extrapolate from marine to air and I know what you mean about the need to use the M word to wake people up in some areas.
Since I was driving a lifeboat I had little need to initiate a Mayday other than for the radio examination, but it was always possible. The only time we could envisage using it was if the boat was inverted and the self righting failed, I am not sure the VHF would have worked with the antenae a meter or 2 underwater, but hey, we had good lifejackets and our mates at base waiting for our return,so no real danger!