"What you just said is ambiguous; it could mean this ... or this..., but I have no way of knowing which is most likely. Could you please clarify what you mean?"
When we flip a coin, it can come up heads or tails, randomly. But when someone is talking ambiguously, tossing a coin to decide what they mean has a 50/50 chance of ending up as a misunderstanding, not what most of us would want.
I know the problem well. My husband has a tendency to speak ambiguously several times a day.