There used to be a gentleman who gave the mandatory safety briefing before taking guests from Lundy Island by helicopter (the only travel option in winter months) who would make the point that if one person inflates their vest, the other passengers would lemming-like inflate their vests and then you suddenly find the cabin is filled with 5 or 6 inflated people that have no chance of getting out of the door. He always used to joke that the whistle was to amuse yourself until the coastguard arrived.