One particularly unique urban legend goes something like this:
On a hot summer night, you turn the fan on and fall asleep. The next morning, you're found dead. The cause? Somehow, the fan has caused your body to shut down overnight.
Sound improbable? Well, that's because it is.
The mechanism behind this urban legend comes in a few different flavors.
Some say that the electric fan pushes air past your body which cools it down. Since you're asleep, your body's natural ability to regulate temperature fails and you suffer hypothermia. Obviously, this makes little sense. If that was true, every person that falls asleep in an environment much lower than 95F would die. Since we're not cold blooded, I think we can rule that one out. There's also the fact that the only cooling that a fan does is through increasing the evaporation rate of sweat.
What about the idea that the fans move air past your face too fast for you to breath in? As a test, try to breath while a fan is blowing in your face.
You're still alive? Good. I think we can rule that one out.
Another belief is that the fan will dehydrate the air and desiccate your body overnight. For those of us that have fallen asleep with a ceiling fan on and not awoken as a mummy, I think we're safe in ruling that one out too. Also, for dehydration to happen from that method, the relative humidity would have to be really low.
Even more perplexing is the idea that the fan blades somehow mechanically cleave the individual oxygen molecules apart rendering them unbreathable. How a diatomic, double-bonded molecule gets broken apart by a plastic fan blade is beyond me.
There's one more idea for how this urban legend: carbon dioxide poisoning. This assumes that carbon dioxide is given off by electric motors as they operate. This is a false assumption because, well, they don't. If it was a gasoline powered ceiling fan then that might work but I don't think I've seen one of those on Amazon.
I'll go with this being completely made up.