You think it’s juvenile to self-censor? Have you never heard and adult use swear-adjacent words when talking? This happens for all sorts of reasons. If you think this is a childish thing to do, then I can only assume social norms are very different where you. I can’t think of any child I know ever self-censoring in this way. They’d either swear, or not swear. But I do know of adults who do it.