Fine? My post makes it perfectly clear that its imposition is less than a remote possibility. But, before others simply ignore the prohibition on USN's entering the US on other nation's passports, it bears mention that it is a violation and could be penalized.

Not sure how much more clear I could have been.

Same thing with the question of whether the agent checking you in is a busy body or not. Sort of silly to tie yourself in knots when your focus should be getting medical testing and treatment if required and when you are already interfacing with the consular process which can issue documents in short order when necessary.