On a sunny summer day a Democrat and a Republican are sitting on a blanket having a picnic. A bird passes overhead, and as birds sometimes do, drops a spot of white feces that lands on the blanket between them. Both move to wipe it away. The stain left behind has a vaguely equine profile.
"Would you look at that," announces the Democrat. "It's raining unicorns!"
The Republican studies the stain for a moment and replies, "looks like bird shit to me."
"Oh, no! It's definitely a unicorn. See, here's the nose and head, here are the ears, here's the mane, and here's the horn. It's definitely raining unicorns."
"Are you crazy?" The Republican insists. "It's a perfectly clear sunny sky, not a cloud to be seen anywhere. How could it possibly be raining, let alone raining unicorns. It's just bird shit."
"Perception is reality!" The Democrat jabs viciously at the stain. "I perceive a unicorn. It fell from the sky. Therefore, it is raining unicorns and you have no right to disagree. What are you, some kind of fascist? What have you got against unicorns?"
"It's bird shit," the Republican says, standing to leave. "Ordinary bird shit. Now you've ruined our peaceful picnic by insisting something impossible is real."
"I have a First Amendment right to say anything I like! You're nothing but a shallow, close-minded, unimaginative bigot. It's a unicorn. Therefore, it is raining unicorns and you cannot prove me wrong."
Shaking his head in disgust, the Republican walks away, leaving the Democrat in complete control of the picnic blanket and remaining food.
"What a lovely day for a picnic!" The Democrat declares loudly to the empty meadow. "And it's even raining unicorns. A perfect picnic!"