BG: Ex and his wife and my new husband and I are all on pleasant terms. We aren't best buds, but we chat pleasantly at events we all attend for the kids, and we meet periodically to discuss kid issues that need addressed as a team.
Several times, I have had the odd situation that in discussing or mentioning anything that happened more than 4 years ago, ex and I were together. So anything I share will involve ex and I as a couple. We were married 10 years, dated for 3, and have only been apart 3, so really the vast majority of my adult life was as part of that couple.
When I am away from ex, as I generally am, I just leave him out of the story and say "when I lived in X place, Y was my favorite part," or "one time on vacation, Z happened to me." But when ex is there, I can't pretend that it happened to just me. I can't say "I" when talking about parenting the kids, it will offend him. But I feel weird mentioning things that happened to US with his new wife there, like she might think I am laying claim to him or trying to make her feel bad. I am not. I just feel my hands are tied for chit-chat if I have to ignore 13 years of my life and the entire babyhood of both of my kids.
This weekend, new wife was telling me she saw a celebrity. I said "that is so cool. The most famous person I ever saw was B when ex and I were in C." Then ex chimed in and we discussed. I seemed OK, but I felt awkward.
So, is it rude to mention? Like if we are at an event and a mother says "Oh, Z has always loved to run since he was a baby," I might reply "I know how you feel, we had to get a leash for R because she never stopped running."