Blood Rainbow
Blood rainbows are rainbows that form out of human hatred and dread. They have the appearance of a rainbow at first, but the closer you get, the redder it gets, until it looks like pure blood. Unlike most rainbows, there are ends to these, but at the end of them, there are Death Unicorn dens, and if you get anywhere near those, there is no chance that you'll survive. I implore you not to do it.
"Hey, dude, is it normal for your eyes to be bleeding like that?"
"Oh, absolutely not! I just happened to look at a blood rainbow :)"
"Oh, okay, you're never going to be able to see again! :)"