"Remember, my pupil... the one thing we phoenixes recognize that all must strive for is negative acknowledgement. Allow me to demonstrate: You're hair looks like bubble gum somepony chewed and spit back out... that's utterly gross. What does you're mom put on that rats nest you call a mane? Toothpaste? Ugggg... I can't even imagine a toothpasty mane, that would be so disastrously distasteful to behold, yet here you are... out of my sight until you return with a cleaner mane, foal."
And then the canon hair of Princess Celestia was conceived.