3. an ill conceived plan that has no chance of coming to fruition
4. something that does not exist in the real, or physical, world
Geezer: …so this “crypto currency”, as you call it, which doesn’t exist in any physical form, is going to revolutionize the way the world transacts business?
Millennial: Yes…exactly.
Geezer: That’s just a unicorn fart in the wind.
A person pretending to be something they aren't, or an impostor. This is inferred because of the old alien movies where alien pods appear on earth and the "pod people" dispose of the humans and slowly reproduce the bodies, pretending to be humans.
The pod person was pretending to be my father, but I knew that he was an alien when he acted differently than my father ever would have.