Mark, some long time ago we were running water samples and bottom profiles in 34F water and a discussion came up about whether to wear life jackets over or under the parkas, and whether it would make any difference anyhow since the ship we were on couldn't round up and come back for you before your lungs froze up in any case.
The wise old man in charge of things said just wear the life jackets, with whatever has the highest visibility on the outside. Not because it will make any difference in how long you live, but simply as a courtesy to those poor SOBs conducting the SAR operations, so they can find your body quickly and go back home again.
The logic still works for me. Someone thinks they're invulnerable, fine, no argument here. But they'd damn well better have the courtesy to make life easier on the SAR guys.
Oddly enough, when they hear "the only difference is how quickly we can recover your body" they start to question the invulnerability aspect as well.