I get really put off when somebody says, “Well, speak of the devil!” I’m like, “You’ve just made our mutual friend materialize by speaking about him, and now you want to discuss the devil? Actually this might not be a bad time to not mention the devil under any circumstances whatsoever. Because I could really go without summoning the fucking devil right now.”
Dude, that whole “speak of the devil” thing extended to its full, unabbreviated glory is “Speak of the devil, and he will appear.”
Basically you’re just saying that your friend, whom you were speaking of and just showed up, is the devil. Or just comparing said friend to the devil. Either way is fine.
I think Sean Penn is writing under the pen name “Casbot.”