Here is my story. I was playing in a flight C GNT district final a while back, we sit down at the beginning of a round and tell our opponents we are playing a strong club system. They have a discussion in a foreign language, presumably about their defense to 1♣. On the second board I pick up something like A8754 KQ4 AKQT7 - and the auction proceeds
At this point I ask about 1♦ and get the unexpected response: "He always bids 1♦."
I am sitting there trying to figure out if this is even a legal agreement when I realize, hey, if they want to give me an extra step in every 1♣ auction, I might as well let them!
I figured I could describe my hand decently by passing here and bidding ♠ over the runout. But LHO had no idea what to do, of course, eventually he decided to pass too. I think he had ♦Jxxx in a flat hand. We lost a couple IMPs when our counterparts made 4♠, so I guess the 1♦ bid worked!
What are your favorite stories about your opponents' weird agreements?