What it is:
Moist just refers to anything that's slightly wet. Over time, it's taken on some sexual overtones, but that has nothing to do with why this word makes America so uncomfortable. It's just a terrible, shit word. No one has any problems with "damp" or "wet" or even "moisture." But moist, on its own, is a nightmare. I've now typed it five times for this article and I still cringe. It never get easier.
Use it in an Awful Sentence:
Take any sentence with the word "moist" in it.
Now imagine that your mom is the one who said it.
What it Actually Calls to Mind:
Because of how awful "moist" is, it should only be used to describe a very specific kind of situation-dampness. Imagine a pale, unshaven, miserable kind of "Indoor Person." He has cold, clammy hands that are always touching you, and there's a ring of wetness around his mouth, because he's either constantly licking his face or he just secretes some kind of acidic creep face-juice. That person can be described as "moist." This is the only kind of human whose creepiness is at a level equal to that of the word moist. Any other time water is involved, the situation is "wet," but this particular mouth-breathing, basement-dwelling breed of human is, without a doubt, moist.