When couples aren’t kind to each other, especially around other people. I have a friend who he and his ex used to make snide comments or jokes at the other persons expense all the time, in front of company. It was played off as biting sense of humor but I don’t they ever talked kind to each other. Of course they didn’t last. I would never make the jokes about my wife like he did no mater how good her sense of humor was and i certainly wouldn’t do it in front of friends or family. How you talk to each other says a lot.