Do not talk trash about Harry Potter to filmmaker, screenwriter, producer, author and former special effects makeup artist Guillermo Del Toro.

While you'll probably never actually need to use that advice, the warning comes after Prisoner of Azkaban director Alfonso Cuarón shared his experience doing just that. Apparently Del Toro is a passionate Potterhead.

It's funny, but the person who directed the Prisoner of Azkaban movie initially scoffed at the idea.

He shared the news of the job offer with Guillermo Del Toro once he was initially offered the project. Cuarón explained he'd never read a Harry Potter book or seen any of the previous films. Apparently his tone was dismissive, almost mocking the project as he talked.

Del Toro was having exactly none of that, because Harry Potter makes Guillermo Del Toro feel like:

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Alfonso Cuarón talked to Vanity Fair about Guillermo's reaction. He was rather "passionate" in his argument.

"I talked with Guillermo, as I always do, and he says, 'What's happening? Any projects going on?'."

"And I said, 'I'm going for Harry Potter, can you believe it?' And I even made fun of it. I hadn't read the books or seen the films."

"And then he looks upset with me. He called me 'flaco'—that means skinny [in English]. He says, 'F^cking flaco, you're such a f^cking arrogant bastard. You are going right now to the f^cking bookshop and get the books and you're going to read them and you call me right away'."

Twitter is having a great time giggling at the situation.

So here's a question: based on how hard Del Toro defended the series, what house do you think he's sorted into?

H/T: Vanity Fair, Gizmodo, Twitter