I think the thought about never taking it off comes from the promise of "whoever dies wearing this scapular..."etc. So some people are so concerned about dying, and so scrupulous, that they literally never take it off unless they have an immediate replacement at hand.
I just recently learned that it's fine to take it off temporarily, for brief periods. When I was performing I belonged to the "never take it off" gang, and had rigged my scapular with somewhat longer nylon fishing line cords so that it would be invisible under a costume. As you can well imagine, my scapulars got pretty gamy pretty fast. In Soho there is a little patch of ground outside my old apartment that has probably a couple hundred old scapulars in varying states of decomposition where the old ones got buried when they got so ripe that I was forced to replace them. I used to buy them by the dozen a couple of times a year. I'm kind of kicking myself now at how neurotic that was!:o But nobody told me otherwise, and I didn't want to risk dropping dead without it on.
I can see where that borders on superstition.
Naturally, if you adhere to the requirements of the scapular, you probably aren't in a state of mortal sin, so you probably wouldn't go to hell anyways. And since you still are enrolled in the Carmelite confraternity, you would probably be able to get the Sabbatine privilege if, for example, your hair dryer fell into the bathtub and electrocuted you while you were taking a bath with your scapular nearby on the vanity. Although I don't know anyone dumb enough to leave a hair dryer plugged in near a bathtub while they were taking a bath! If there's anyone smarter than me that can explain it, I'd be interested in hearing it.
Thinking it through a little further, I doubt Mary would ask us to do anything that flies in the face of common sense, or anything onerous. The entire point of the scapular was to provide an easy reminder of devotion to her, not a rigorous set of rules that we had to conform with or hoops we had to jump through.
Nowadays, I take mine off when I do strenuous exercise, when I shower, or when I go to bed.