we say speak of the devil quite a bit – it’s become a part of everyday lexicon when you’re talking about someone and that person shows up.
but the phrase goes back to 1600s or even earlier. and it wasn’t meant lightheartedly, either, like we mean today. the full phrase is:
“speak of the devil and he will appear.”
it originated in england and it was pretty serious stuff. there was a superstitious belief that it was dangerous to mention the devil by name. at that time, it was like speaking the name of god. this is how all the devil’s nicknames came to be: prince of darkness, the horned one, etc. it seems like the clergy was a little more adamant about the situation than the general populace. no one actually thought the devil would appear, but it was considered unlucky.
that’s changed, though, and when we say speak of the devil, it’s usually a pretty ok thing to say and no one’s expecting the devil to show up.
though i’d be pretty stoked if the devil duck showed up.