After an A I believe it is difficult to not want to become the A police, but until there is truth and fact behind what you speak about it is only gossip.
Oh, there is truth and fact behind it. I just don't have physical proof I can show the OBS. For instance, this other couple went on a weekend trip with WH and MOW. It was supposed to be four friends/co-workers doing a race together that was far enough away so they needed to spend the night. I found out afterwards that instead of the sleeping arrangements being MOW/OMOW and WH/OMOM, it was MOW/WH and OMOW/OMOM. There was at least one other situation where the same sort of thing happened.
I don't really just run into either of the OBS so I wouldn't have an opportunity to work it into conversation the way the other poster's boss's wife did, or I would definitely try something like that.