I had heard that you shouldn’t talk about the vacations you took, about how smart your kid is, etc., because it will arouse ayin hara in the person you are talking to. You will share in the blame if the other person is caused to think about why is this guy so lucky or fortunate? You cause them to be judged, and are judged in turn.
In practical terms, it is hard to not kvell over a sister’s upcoming marriage. We are simply expected to have some sensitivity about whether this news might cause some small amount of jealousy or annoyance or resentment. Watching what you say goes farther to protecting you from ayin hara than something you wear.