This is not quite what you want, but if you are a grad student giving a talk and a senior person prefaces her question to you with "I am confused about...", you are likely talking nonsense and they are too polite to tell you straight up.
Alternatively "I may hve misunderstood but surely...." is a good way to couch an objection
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.