Quoth the raven, "Nevermore!"

I mentioned the no costume rule for today. But a certain teacher dresses up each year for a poetry lesson she does on Halloween.
And another teacher hassled her a bit about it and said, "I thought we weren't supposed to wear costumes today."

So this certain teacher said, "I don't know about any of that. I'm a sub. My name is Mr. Poe."

Any guesses?