He offhandedly told someone he didn't like mushrooms.
My ex husband tried my friends stuffed mushrooms and seemed to like them, so I offered to give them a try at home. In our tiny kitchen and very limited kitchenware, making them was labor intensive. We were also very poor, so to afford ingredients I would have to hand wash all of our laundry and save my quarters (he was a mechanic and his clothes were repulsive). He would ask me for them often when we'd have a tough day at work or I'd offer to make him something special and ask what he was in the mood for. When I heard him say he didn't like mushrooms I questioned him later when we were alone, where he admitted he didn't like the stuffed mushrooms and just said he did because he thought I wanted him to like them??? I made them for him bedbugs we had a really fucking hard life and were so poor, and I just wanted to do something nice so our lives didn't suck so hard. He knew I had to wash our clothes in the bathtub and save grocery money when I did special dinners and that it was more money and more work for less food than many other things he actually liked.
I found him in a ton of other lies. He had spent years telling me what he thought I wanted to hear. Some of it was important, a lot of it was really stupid stuff like the mushrooms. He had curated this entire personality. Once I caught on I would question him more and make him give his opinion first on almost everything new because I didn't want him to just mirror me. He started being super vague and if he gave an opinion different from mine he would start back tracking as soon as I spoke. I would get upset and tell him we could just disagree on something and didn't have to think the same about literally everything.
Everything fell apart, it never got better and he never worked to communicate. I felt like I was constantly playing 20 questions and it would take so much work to find out things like the music he actually liked, the food he actually liked, what he actually wanted out of life. And if I didn't also like or want those things he would melt down.
There were so many problems by the end of our relationship, but his insistence on lying was definitely the stupidest. My partner now has a lot of similar and a lot of different opinions and tastes from me, and is never afraid to share them. It is so refreshing to be with someone who can give their opinion on things that are big or small and isn't trying to trick me into thinking we have everything in common. I think my ex was afraid of me leaving but his lying and manipulation got over the top and he became a self fulfilling prophecy.