A friend/coworker of mine and his wife hosted a weekly boardgame night that I attended. Most of the other guests were kinda flaky, and this one particular day, I was the only one who showed up. So it was just me, my friend, and his wife.
Someone suggested Dixit, which I had never played before, but it sounded fun and I was down to play. So we broke it out, shuffled, and started the game.
Now, if you don't know how Dixit works, it's basically a deck of cards with pictures on them. One of a toy abacus. Another of a child pointing a toy sword at a dragon. Another of a winding staircase with a snail at the bottom. Etc.
In one version of the game similar to Apples to Apples or Scategories, everyone gets a hand of cards which they keep hidden. The dealer announces a clue and everyone (including the dealer) contributes a card from their hands face-down to the center of the table and the dealer shuffles them together and reveals them all at once without revealing whose card is whose. Then players vote which one they think matches the clue. You get points as a player if others vote for your card or if you vote for the one the dealer picked. As a dealer, you get points if close to 50% of the players vote for yours.
I was the dealer this round. One of the cards in my hand was of a ship's anchor. That's when it came to me.
See, the friend/coworker and I both worked in web software development. His wife didn't. And I came up with the perfect play. I gave the clue "hyperlink." Hyperlinks on web pages are created using the HTML <a> tag. The "a" stands for "anchor." And any web developer would know that.
When the vote came in, I got one vote for my card from my friend and his wife failed to select the correct card and so didn't get any points. It was a slam dunk move. But I felt a little bad for excluding my friend's wife from an inside-knowledge thing.
The next round, my friend was the dealer and he picked a rule/card that was an inside-knowledge thing between the two of them. (A line from a poem they both knew well, the next line of which related to the picture of the card.) So I was glad of that.
It was definitely legit in the sense of it being something completely counterable by my friend had she been looking out for it, and it certanly wasn't an exploit. It did still feel dirty to make use of information that she hadn't noticed to get her to defeat herself, particularly since it only worked by me carefully not saying anything about it for as long as it took to do
Religion victories in Civ are poorly telegraphed in general. You can easily look at the minimap and see that someone is conquering everything, and poking at a player's borders will show you that they're technologically advanced, but religion and culture victories tend to sneak up on people.