OP, you're setting a very high standard that most folks do not. So if this is something you're going to insist upon, it's going to take many iterations of telling people your rules. Remember that there will likely be costs to insisting on this standard, including what others here have already pointed out: that folks will think you're a tad bit anal, anxious, and uptight. And unfriendly. And untrusting,
So... well, just give it your best, most diplomatic shot. Over and over and over again, because this is not the kind of thing that will come naturally to people.
Maybe you can say it like: We don't share toothbrushes and we don't share spoons, forks, or eat off other people's fingers. (How you'll explain why YOU do this but not them? Call the UN diplomatic corps for help with this one!

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